apple-gmux: Fix up the suspend/resume patch

I incorporated the wrong version of the suspend/resume patch for gmux,
and so lost David Woodhouse's fix to leave the backlight level unchanged
over suspend/resume. This fixes it up to v2.

Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/apple-gmux.c

@@ -88,7 +88,7 @@ static int gmux_update_status(struct backlight_device *bd)
 	u32 brightness = bd->props.brightness;
 
 	if (bd->props.state & BL_CORE_SUSPENDED)
-		brightness = 0;
+		return 0;
 
 	/*
 	 * Older gmux versions require writing out lower bytes first then