msm: vidc: Update video clock flags

Set CLKFLAG_RETAIN flags during every clock prepare. Also
Set CLKFLAG_NORETAIN flags during unprepare to make flag
operations symmetric.

CRs-Fixed: 2035342
Change-Id: I072985743d8ee0d5f62b25b3be3f80caf29cda17
Signed-off-by: Praneeth Paladugu <ppaladug@codeaurora.org>