pinctrl/abx500: prevent error path from corrupting returning error

pinctrl/abx500: prevent error path from corrupting returning error

Prior to this patch abx500_gpio_probe() would return the return-value
of gpiochip_remove() during its error patch regardless of what the
actual failure was. So as long as gpiochip_remove() succeeded, probe()
would look like it succeeded too.

This patch ensures the correct error value is returned and that
mutex_destroy() is invoked if gpiochip_add_pin_range() were to fail.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>