Fix some AB3100 regulator issues

This patch will remove surplus register writes on shut down of
LDO D (this magic was not needed), remove an unnecessary (!) error
check and really unregister the regulators when the module is
unloaded.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>