pinctrl/nomadik: use devm_* allocators for gpio probe

The GPIO portions of the Nomadik pinctrl driver was not using
the managed devm_* interfaces, lets' use them consequently and
cut down the error path and special case handling.

Acked-by: Patrice Chotard <patrice.chotard@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>