sony-laptop: fix sparse non-ANSI function warning

Fix sparse warning for non-ANSI function declaration:

drivers/platform/x86/sony-laptop.c:1134:35: warning: non-ANSI function declaration of function 'sony_nc_rfkill_update'
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc:	Matthew Garrett <mjg@redhat.com>
Cc:	Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/sony-laptop.c

@@ -1131,7 +1131,7 @@ static int sony_nc_setup_rfkill(struct acpi_device *device,
 	return err;
 }
 
-static void sony_nc_rfkill_update()
+static void sony_nc_rfkill_update(void)
 {
 	enum sony_nc_rfkill i;
 	int result;