pinctrl/nomadik: simplify GPIO probe

Instead of jumping to a label later in the probe just return
with an error code whenever probe() fails. Make sure to remove
the gpiochip on irqdomain error now that we're at it.

Reviewed-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>