regulator: rpi-panel-attiny: Use backlight helper

backlight_properties.fb_blank is deprecated. The states it represents
are handled by other properties; but instead of accessing those
properties directly, drivers should use the helpers provided by
backlight.h.

Instead of retrieving the backlight brightness in struct
backlight_properties manually, and then checking whether the backlight
should be on at all, use backlight_get_brightness() which does all
this and insulates this from future changes.

Signed-off-by: Stephen Kitt <steve@sk2.org>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220607185304.1128962-1-steve@sk2.org
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/rpi-panel-attiny-regulator.c

@@ -187,15 +187,11 @@ static int attiny_update_status(struct backlight_device *bl)
 {
 	struct attiny_lcd *state = bl_get_data(bl);
 	struct regmap *regmap = state->regmap;
-	int brightness = bl->props.brightness;
+	int brightness = backlight_get_brightness(bl);
 	int ret, i;
 
 	mutex_lock(&state->lock);
 
-	if (bl->props.power != FB_BLANK_UNBLANK ||
-	    bl->props.fb_blank != FB_BLANK_UNBLANK)
-		brightness = 0;
-
 	for (i = 0; i < 10; i++) {
 		ret = regmap_write(regmap, REG_PWM, brightness);
 		if (!ret)