greybus: fix pointless null check

Coccinelle points out that a call in gb_lights_channel_free() to
flush_work() is passed which is always non-null.   Prior to the
call, there is an unnecessary check to see if that address is null.
Get rid of the test.
Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/light.c

@@ -1019,8 +1019,7 @@ static int gb_lights_light_register(struct gb_light *light)
 static void gb_lights_channel_free(struct gb_channel *channel)
 {
 #ifndef LED_HAVE_SET_BLOCKING
-	if (&channel->work_brightness_set)
-		flush_work(&channel->work_brightness_set);
+	flush_work(&channel->work_brightness_set);
 #endif
 	kfree(channel->attrs);
 	kfree(channel->attr_group);