HID: ishtp-hid-client: Fix 'suggest-attribute=format' compiler warning

Fixes the following W=1 kernel build warning(s):

 drivers/hid/intel-ish-hid/ishtp/bus.c: In function ‘ishtp_trace_callback’:
 drivers/hid/intel-ish-hid/ishtp/bus.c:876:29: warning: return type might be a candidate for a format attribute [-Wsuggest-attribute=format]
 876 | return cl_device->ishtp_dev->print_log;
 | ~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~

Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: Daniel Drubin <daniel.drubin@intel.com>
Cc: linux-input@vger.kernel.org
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

drivers/hid/intel-ish-hid/ishtp-hid-client.c

@@ -784,7 +784,7 @@ static void hid_ishtp_cl_reset_handler(struct work_struct *work)
 	}
 }
 
-void (*hid_print_trace)(void *unused, const char *format, ...);
+ishtp_print_log ishtp_hid_print_trace;
 
 /**
  * hid_ishtp_cl_probe() - ISHTP client driver probe
@@ -823,7 +823,7 @@ static int hid_ishtp_cl_probe(struct ishtp_cl_device *cl_device)
 
 	INIT_WORK(&client_data->work, hid_ishtp_cl_reset_handler);
 
-	hid_print_trace = ishtp_trace_callback(cl_device);
+	ishtp_hid_print_trace = ishtp_trace_callback(cl_device);
 
 	rv = hid_ishtp_cl_init(hid_ishtp_cl, 0);
 	if (rv) {

drivers/hid/intel-ish-hid/ishtp-hid.h

@@ -16,9 +16,9 @@
 #define	IS_RESPONSE	0x80
 
 /* Used to dump to Linux trace buffer, if enabled */
-extern void (*hid_print_trace)(void *unused, const char *format, ...);
+extern ishtp_print_log ishtp_hid_print_trace;
 #define hid_ishtp_trace(client, ...) \
-		(hid_print_trace)(NULL, __VA_ARGS__)
+	(ishtp_hid_print_trace)(NULL, __VA_ARGS__)
 
 /* ISH HID message structure */
 struct hostif_msg_hdr {

drivers/hid/intel-ish-hid/ishtp/bus.c

@@ -869,9 +869,9 @@ EXPORT_SYMBOL(ishtp_get_pci_device);
  *
  * This interface is used to return trace callback function pointer.
  *
- * Return: void *.
+ * Return: *ishtp_print_log()
  */
-void *ishtp_trace_callback(struct ishtp_cl_device *cl_device)
+ishtp_print_log ishtp_trace_callback(struct ishtp_cl_device *cl_device)
 {
 	return cl_device->ishtp_dev->print_log;
 }

drivers/hid/intel-ish-hid/ishtp/ishtp-dev.h

@@ -10,6 +10,7 @@
 
 #include <linux/types.h>
 #include <linux/spinlock.h>
+#include <linux/intel-ish-client-if.h>
 #include "bus.h"
 #include "hbm.h"
 
@@ -202,8 +203,7 @@ struct ishtp_device {
 	uint64_t ishtp_host_dma_rx_buf_phys;
 
 	/* Dump to trace buffers if enabled*/
-	__printf(2, 3) void (*print_log)(struct ishtp_device *dev,
-					 const char *format, ...);
+	ishtp_print_log print_log;
 
 	/* Debug stats */
 	unsigned int	ipc_rx_cnt;

include/linux/intel-ish-client-if.h

@@ -8,11 +8,17 @@
 #ifndef _INTEL_ISH_CLIENT_IF_H_
 #define _INTEL_ISH_CLIENT_IF_H_
 
+#include <linux/device.h>
+#include <linux/uuid.h>
+
 struct ishtp_cl_device;
 struct ishtp_device;
 struct ishtp_cl;
 struct ishtp_fw_client;
 
+typedef __printf(2, 3) void (*ishtp_print_log)(struct ishtp_device *dev,
+					       const char *format, ...);
+
 /* Client state */
 enum cl_state {
 	ISHTP_CL_INITIALIZING = 0,
@@ -76,7 +82,7 @@ int ishtp_register_event_cb(struct ishtp_cl_device *device,
 /* Get the device * from ishtp device instance */
 struct device *ishtp_device(struct ishtp_cl_device *cl_device);
 /* Trace interface for clients */
-void *ishtp_trace_callback(struct ishtp_cl_device *cl_device);
+ishtp_print_log ishtp_trace_callback(struct ishtp_cl_device *cl_device);
 /* Get device pointer of PCI device for DMA acces */
 struct device *ishtp_get_pci_device(struct ishtp_cl_device *cl_device);