gpio: squelch a compiler warning

drivers/gpio/gpiolib-of.c: In function 'of_gpiochip_find_and_xlate':
drivers/gpio/gpiolib-of.c:51:21: warning: assignment makes integer from
pointer without a cast [enabled by default]
   gg_data->out_gpio = ERR_PTR(ret);
                     ^
this was introduced in d1c34491

the upstream kernel changed the type of out_gpio from int to struct gpio_desc *
as part of a larger refactoring that wasn't backported

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>