gpiolib: Consistent use of ->get_direction() inside gpiolib

Two out of three calls to ->get_direction (excluding, of course,
gpiod_get_direction() itself) are using gpiod_get_direction() and
one is still open coded.

Replace the latter one to use same API for sake of consistency.

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