msm: vidc: Avoid memset of list elements in the buffer entry.

- Due to race condition between free buffer and flush output buffers,
  invalid buffer is getting accessed sometimes.
- Reset all the members in buffer entry except list elements.

(cherry picked from commit 8105df366cf6b9f1ddbc15d561fb6a5f12540416)
CRs-Fixed: 411197

Change-Id: Id95037f57d7fe4bc88b96f187953194ec838d63b
Signed-off-by: Srinu Gorle <sgorle@codeaurora.org>
Signed-off-by: Neha Pandey <nehap@codeaurora.org>