msm: vidc: Free buffer pool entry and then delete address table

Free the buffer pool entry first and then delete the
address table (which will unmap the buffer with iommu)
else we might get a corner case where the entry was not
freed but the buffer is unmapped and the next buffer is
mapped with the same physical address which is still
available in the buffer pool entry, which results in
video recording failure.

Change-Id: I6978d5e5de35db63f43a7f38c58940216217b676
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>