regulator: max8973: Let core handle GPIO descriptor

The probe path of this driver is a bit complex: sometimes the
GPIO descriptor is passed to the regulator core, sometimes
it is not.

To handle it in a simple way: stick with the devm_* resource
management and unhinge the GPIO descriptor devres handling
right before passing it to the regulator core, if we pass it
to the regulator core.

Fixes: e7d2be69 ("regulator: max8973: Pass descriptor instead of GPIO number")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>