regulator: mt6311: Drop useless header

The mt6311 includes the legacy header <linux/gpio.h> for no
reason, drop the include.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230808-descriptors-regulator-v1-6-939b5e84dd18@linaro.org


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