regulator: add snapshot of the stub-regulator driver

This is a snapshot of the stub-regulator driver as of msm-4.4
commit 1f1574bb1837 ("ASoC: wcd9335: Fix traversing of source
dapm widgets")

Correct minor checkpatch issues as well.

Change-Id: Ia73d245419e44d74712b813e58de1973112233c4
Signed-off-by: David Collins <collinsd@codeaurora.org>
Signed-off-by: Harry Yang <harryy@codeaurora.org>