msm: vidc: fix deadlock between queue and flush buffer handling

qbuf ioctl acquired bufq[port].lock in one thread and flush
call acquired registeredbufs.lock in another thread. So
thread-1 is waiting for registeredbufs.lock & thread-2 is
waiting for bufq[port].lock i.e leading to deadlock. So
added change to avoid above mentioned deadlock.

Change-Id: Ie21984fdb562ca7a09f801f036f3a78429ceab94
Signed-off-by: Govindaraj Rajagopal <grajagop@codeaurora.org>