msm: vidc: fix lock issue in msm_comm_get_mbs_per_sec()

Forward thread acquired v4l2_ctrl->handler->lock in
v4l2_s_ctrl() and waiting for response from response thread.
Response thread was blocked on core->lock which was acquired
by second forward thread. The second forward thread acquired
core->lock and called v4l2_g_ctrl() in msm_comm_get_mbs_per_sec()
where it was blocked on same v4l2_ctrl->handler->lock and hence
response thread was not unblocked. Resolve the deadlock issue
by avoiding v4l2_g_ctrl() call in msm_comm_get_mbs_per_sec().

CRs-Fixed: 1095539
Change-Id: I73c2a74f1bb86f2b0359be54ed4f7675051db7b0
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>