rtc: rx6110: Remove unused of_gpio,h

of_gpio.h provides a single function, which is not used in this driver.
Remove unused header.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230215165030.83621-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>