regulator: rpi-panel-v2: Cache regmap values

Not all implementations of the V2 regulator support reading back
the value of registers, which makes the GPIO control fail.
Enable the regmap caching to avoid this.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>

Author: 6by9

drivers/regulator/rpi-panel-v2-regulator.c

@@ -33,6 +33,7 @@ static const struct regmap_config rpi_panel_regmap_config = {
 	.val_bits = 8,
 	.max_register = REG_PWM,
 	.can_sleep = true,
+	.cache_type = REGCACHE_MAPLE,
 };
 
 static int rpi_panel_v2_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,