backlight: lm3630a: Turn off both led strings when display is blank

Use backlight_is_blank() to determine if the led strings should be turned
off in the update_status() functions of both strings.

Signed-off-by: Maximilian Weigand <[e-mail]>
Reviewed-by: Daniel Thompson <[e-mail]>
Reviewed-by: Sam Ravnborg <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/video/backlight/lm3630a_bl.c

···
 	usleep_range(1000, 2000);
 	/* minimum brightness is 0x04 */
 	ret = lm3630a_write(pchip, REG_BRT_A, bl->props.brightness);
-	if (bl->props.brightness < 0x4)
+
+	if (backlight_is_blank(bl) || (backlight_get_brightness(bl) < 0x4))
+		/* turn the string off  */
 		ret |= lm3630a_update(pchip, REG_CTRL, LM3630A_LEDA_ENABLE, 0);
 	else
 		ret |= lm3630a_update(pchip, REG_CTRL,
···
 	usleep_range(1000, 2000);
 	/* minimum brightness is 0x04 */
 	ret = lm3630a_write(pchip, REG_BRT_B, bl->props.brightness);
-	if (bl->props.brightness < 0x4)
+
+	if (backlight_is_blank(bl) || (backlight_get_brightness(bl) < 0x4))
+		/* turn the string off  */
 		ret |= lm3630a_update(pchip, REG_CTRL, LM3630A_LEDB_ENABLE, 0);
 	else
 		ret |= lm3630a_update(pchip, REG_CTRL,