mfd: intel_soc_pmic: Do not mangle error code from devm_gpiod_get_index()

It is usually better to pass actual error code from a function call than
mangling it to another.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>