regulator: core: fix race condition in regulator_put()

commit 83b0302d upstream.

The regulator framework maintains a list of consumer regulators
for a regulator device and protects it from concurrent access using
the regulator device's mutex lock.

In the case of regulator_put() the consumer is removed and regulator
device's parameters are updated without holding the regulator device's
mutex. This would lead to a race condition between the regulator_put()
and any function which traverses the consumer list or modifies regulator
device's parameters.
Fix this race condition by holding the regulator device's mutex in case
of regulator_put.

Signed-off-by: Ashay Jaiswal <ashayj@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
[lizf: Backported to 3.4:
 - adjust context
 - no need to change the comment]
Signed-off-by: Zefan Li <lizefan@huawei.com>