mfd: mc13xxx: Stop including of_gpio.h

Neither SPI nor I2C variant uses any APIs from of_gpio.h so let's stop
including it.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20220926054421.1546436-1-dmitry.torokhov@gmail.com