msm: camera_v2: Post fd close event to user space.

Post the stream destroy event to back-end even if the last
fd is being closed. This is required because when the mediaserver
crashes, the fds are closed in no particular order.

Change-Id: Ie6098f9aa2b9090d9901684998a8ab3a332d4805
Signed-off-by: Ankit Premrajka <ankitp@codeaurora.org>