video: msm: Wait for latest histogram data

Old histogram API introduced behavior that calls to collect histogram data
would return a frame's histogram once, and would wait until new data was
available if needed. Follow old histogram behavior by waiting when
histogram has old/not ready data.

Change-Id: Ia1b6b5b7a5b63a570a641b5460eb8e0d72c458c8
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>