regulator: rpi-panel-attiny: Drop useless header

The RPI panel regulator driver includes the legacy header
<linux/gpio.h> for no reason, this is a driver and <linux/gpio/driver.h>
is already included. Drop the include.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230808-descriptors-regulator-v1-3-939b5e84dd18@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>