staging: mt7621-gpio: use ternary operator in return in mediatek_gpio_get_direction

This commits replaces if statement and two returns in favour
of a only one return using a ternary operator.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>