msm: camera: Correct the usage of return free buffer API.

When a free buffer is released/returned back from userspace,
mark it as QUEUED instead of UNUSED. This will ensure that the
buffer is put back into circulation.

Change-Id: Ib6fc058ee2f34044446e777a525f81b2ee971c9c
Signed-off-by: Kiran Kumar H N <hurlisal@codeaurora.org>