msm: vidc: Fix wait timeout issue

If client has not unregistered any registered buffers
then driver attempts to unregister the buffers with
video firmware in msm_cvp_inst_deinit(). If the buffer
is removed from the registered buffer list before waiting
for the unregister buffer done event from video firmware
results in wait timeout error. Hence do not remove buffer
from the register buffer list before waiting but remove
after waiting is over to resolve the error.

Change-Id: Iea41de3caf137fb9f138f9a73bbdeb56793584c6
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>