regulator: wm8994: Fix shared GPIOs

This reverts commit 3c6b38d4 "regulator: wm8994: Pass
descriptor instead of GPIO number" as it has problems with shared
GPIOs similar to that on s2mps11.

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>