gpio: fix getting nonexclusive gpiods from DT

Since commit ec757001 ("gpio: Enable nonexclusive gpiods from DT
nodes") we are able to get GPIOD_FLAGS_BIT_NONEXCLUSIVE marked gpios.
Currently the gpiolib uses the wrong flags variable for the check. We
need to check the gpiod_flags instead of the of_gpio_flags else we
return -EBUSY for GPIOD_FLAGS_BIT_NONEXCLUSIVE marked and requested
gpiod's.

Fixes: ec757001 gpio: Enable nonexclusive gpiods from DT nodes
Cc: stable@vger.kernel.org
Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
[Bartosz: the function was moved to gpiolib-of.c so updated the patch]
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>