ieee802154: mcr20a: Remove unused of_gpio.h

of_gpio.h is deprecated and subject to remove.
The driver doesn't use it, simply remove the unused header.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Message-ID: <20240304175320.1199496-1-andriy.shevchenko@linux.intel.com>
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>