HID: intel-ish-hid: add printf attribute to print_log()

Structure ishtp_device contains a logging function, print_log(), which
formats some of its parameters using vsnprintf(). Add a __printf
attribute to this function field (and to ish_event_tracer()) in order to
detect at compile time issues related to the printf-like formatting.

While at it, make format parameter a const pointer as print_log() is not
supposed to modify it.
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Acked-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

drivers/hid/intel-ish-hid/ipc/pci-ish.c

@@ -47,7 +47,8 @@ MODULE_DEVICE_TABLE(pci, ish_pci_tbl);
  *
  * Callback to direct log messages to Linux trace buffers
  */
-static void ish_event_tracer(struct ishtp_device *dev, char *format, ...)
+static __printf(2, 3)
+void ish_event_tracer(struct ishtp_device *dev, const char *format, ...)
 {
 	if (trace_ishtp_dump_enabled()) {
 		va_list args;

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

@@ -238,7 +238,8 @@ struct ishtp_device {
 	uint64_t ishtp_host_dma_rx_buf_phys;
 
 	/* Dump to trace buffers if enabled*/
-	void (*print_log)(struct ishtp_device *dev, char *format, ...);
+	__printf(2, 3) void (*print_log)(struct ishtp_device *dev,
+					 const char *format, ...);
 
 	/* Debug stats */
 	unsigned int	ipc_rx_cnt;