gpio: moxart: Avoid forward declaration

Slightly adjust the code to avoid forward declaration as we need to call
moxart_gpio_set() in moxart_gpio_direction_output() to properly set the
output state.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>