regulator: rpi-panel: Ensure the backlight is off during probe.

The initial state of the Atmel is not defined, so ensure the
backlight PWM is set to 0 by default.
Signed-off-by: NDave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: NDetlev Casanova <detlev.casanova@collabora.com>
Link: https://lore.kernel.org/r/20220124220129.158891-5-detlev.casanova@collabora.comSigned-off-by: NMark Brown <broonie@kernel.org>

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

@@ -250,6 +250,7 @@ static int attiny_i2c_probe(struct i2c_client *i2c,
 
 	regmap_write(regmap, REG_POWERON, 0);
 	msleep(30);
+	regmap_write(regmap, REG_PWM, 0);
 
 	config.dev = &i2c->dev;
 	config.regmap = regmap;