dell-laptop: make dell_laptop_i8042_filter() static

Make dell_laptop_i8042_filter() static as it's used only in dell-laptop.c
Signed-off-by: NAxel Lin <axel.lin@gmail.com>
Signed-off-by: NMatthew Garrett <mjg@redhat.com>

drivers/platform/x86/dell-laptop.c

@@ -473,7 +473,7 @@ static struct backlight_ops dell_ops = {
 	.update_status  = dell_send_intensity,
 };
 
-bool dell_laptop_i8042_filter(unsigned char data, unsigned char str,
+static bool dell_laptop_i8042_filter(unsigned char data, unsigned char str,
 			      struct serio *port)
 {
 	static bool extended;