regulator: core: avoid deadlock in QTI addition to regulator_unregister()

regulator_unregister() calls rdev_free_qti_debugfs() with the
regulator_list_mutex held.  rdev_free_qti_debugfs() then calls
regulator_put() which attempts to lock regulator_list_mutex again.
This leads to deadlock.

Modify regulator_unregister() and rdev_free_qti_debugfs() so that
mutex deadlock cannot occur.

Change-Id: I12bb4c704f7d9332e790c707aba854e224474bdb
Signed-off-by: David Collins <collinsd@codeaurora.org>