regulator: Properly register dummy regulator driver

Recent changes in the driver core appear to mean that the data structures
for the driver core are not fully initialised unless the driver is bound.
Make sure the driver core knows the dummy driver is in use by binding it
to a driver.

Change-Id: I56a14e862c1bab334124072e1a850e8cff9afb12
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Michael Bohan <mbohan@codeaurora.org>