soc: msm-pcm: Added lock in controls _put() and _get() callback

There is race condition around private data used in put() and get()
of few mixer ctls with close() callback. Added global mutex lock and
code changes to protect such critical section by accessing such lock.

Change-Id: I276c2a234cfcbef88b4272b945e5c3f121e8eb32
Signed-off-by: Soumya Managoli <smanag@codeaurora.org>