msm: vidc: Fix cache invalidation issue

- Cache invalidation is being skipped out on all output
  buffers except first buffer due to NULL buffer handle
  in case of all output buffers are allocated as single
  chunk.
- This change fixes the issue by properly assigning the
  buffer handle for all output buffers.

CRs-Fixed: 581806
Change-Id: I415c3cc0ef9d82ea3c97ea618babbfbfc9f36f8b
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>