video: msm: Avoid waking readers on failed histogram copy

Avoid waking up the waiting histogram reader when the current histogram has
failed to copy. Additionally, clean up initialization of histogram
workqueue (was initialized twice).

CRs-Fixed: 361640
Change-Id: I376c0193b8e34aba5b0aef54feb9504f450ffff4
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>