backlight: lp8788_bl: Delete a check before backlight_device_unregister()

The backlight_device_unregister() function tests whether its argument
is NULL and then returns immediately. Thus the test around the call is
not needed.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/video/backlight/lp8788_bl.c

@@ -221,8 +221,7 @@ static void lp8788_backlight_unregister(struct lp8788_bl *bl)
 {
 	struct backlight_device *bl_dev = bl->bl_dev;
 
-	if (bl_dev)
-		backlight_device_unregister(bl_dev);
+	backlight_device_unregister(bl_dev);
 }
 
 static ssize_t lp8788_get_bl_ctl_mode(struct device *dev,