regulator: max77686: Let core handle GPIO descriptor

Use the gpiod_get_from_of_node() rather than the devm_*
version so that the regulator core can handle the lifecycle
of these descriptors.

Fix up the errorpath so that we free this descriptor if
an error occurs in the callback. Rely on the regulator
core to deal with it after this point: a previous patch
fixed up the regulator core to properly dispose any
GPIO descriptors once you call regulator_register().

Fixes: 96392c3d

 ("regulator: max77686: Pass descriptor instead of GPIO number")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>