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 <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/acpi/event.c

···
  *
  */
 
+#define pr_fmt(fmt) "ACPI: " fmt
+
 #include <linux/spinlock.h>
 #include <linux/export.h>
 #include <linux/proc_fs.h>
···
 	/* 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;
 }