gpio: davinci: Remove duplicate assignment of of_gpio_n_cells

The of_gpio_n_cells default is 2 when ->of_xlate() callback is
not defined. No need to assign it explicitly in the driver.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>