gpiolib: Remove duplicative check in gpiod_find_and_request()

The gpiod_find_by_fwnode() already checks for NULL and returns
correct error code in case fwnode is invalid. Drop the respective
check and assignment in the gpiod_find_and_request().

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