regulator: Fix deadlock on removal of regulators with supplies

If a regulator with a supply is being unregistered we will call
regulator_put() to release the supply with the regulator_list_mutex held
but this deadlocks as regulator_put() takes the same lock. Fix this by
releasing the supply before we take the mutex in regulator_unregister().

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>