gpiolib: Initialize gdev field before is used

gpio_hog depends on gdev field being initialized. This patch fixes an
OOPs during initialization of TI's AM335x-ICEv2.

Fixes: 3edfb7bd ("gpiolib: Show correct direction from the beginning")
Tested-by: Vignesh R <vigneshr@ti.com>
Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>