regulator: s2mps11: Pass descriptor instead of GPIO number

Instead of passing a global GPIO number for the enable GPIO, pass
a descriptor looked up with the standard devm_gpiod_get_optional()
call.

This regulator supports passing platform data, but enable/sleep
regulators are looked up from the device tree exclusively, so
we can need not touch other files.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Tested-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>