When regulator_register fails and exits through the scrub path the
regulator_put function was called whilst holding the
regulator_list_mutex, causing deadlock.

This patch adds a private version of the regulator_put function which
can be safely called whilst holding the mutex, replacing the
aforementioned call.
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>