gpio: MOXA ART: rename moxart_gpio_base to base

Renaming "moxart_gpio_base" to "base" allows better fit,
remove line breaks in moxart_gpio_get().

While doing trivial cleanup, also remove fields initialized
with zero in moxart_template_chip.

Signed-off-by: Jonas Jensen <jonas.jensen@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>