regulator: core: Reduce rdev locking region when releasing regulator

When we release a regulator we need to remove references to it from the
rdev which means locking the rdev.  Currently we also free resources
associated with the regulator inside the rdev lock but there is no need
to do this, we can reduce the region the lock is held by restricting it
to just actions that affect the rdev.

Signed-off-by: Mark Brown <broonie@kernel.org>