msm: camera: Do node close with lock before reducing open index

Do session/stream node destroy with lock before
reducing opn_idx to avoid conflicts while closing
node and mutex getting destroyed while other node
still holds it, Also trigger the stream delete to
backend for nodes which are only created by HAL.

CRs-Fixed: 971839
Change-Id: Iefc1132e5790d8f7ba025ee140e536a2b3ca21c0
Signed-off-by: Hariram Purushothaman <hariramp@codeaurora.org>