ACPI: event: Use pr_*() macros to replace printk()

Introduce pr_fmt() and replace direct printk() invocation with
the matching pr_*() call to prepare for removing PREFIX.
Signed-off-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/event.c

@@ -7,6 +7,8 @@
  *
  */
 
+#define pr_fmt(fmt) "ACPI: " fmt
+
 #include <linux/spinlock.h>
 #include <linux/export.h>
 #include <linux/proc_fs.h>
@@ -173,8 +175,8 @@ static int __init acpi_event_init(void)
 	/* create genetlink for acpi event */
 	error = acpi_event_genetlink_init();
 	if (error)
-		printk(KERN_WARNING PREFIX
-		       "Failed to create genetlink family for ACPI event\n");
+		pr_warn("Failed to create genetlink family for ACPI event\n");
+
 	return 0;
 }