msm: display: 8092: Handle no buffer case for VPU composition

Handle the case when the buffer is not queued to MDP. Since in
mpq, the buffers are queued through VPU, so need to make sure
that the configuration are kept even if there is no buffer is
queued.

Change-Id: Ic50c2ccf796998c95de61edb5555bc4047b02dff
Signed-off-by: Ken Zhang <kenz@codeaurora.org>
Signed-off-by: Zohaib Alam <zalam@codeaurora.org>