msm: vidc: Invalidate cache when allocating buffers

We need to remove stale entries in the cache when allocating buffers, as
the ION driver doesn't invalidate the cache.

CRs-Fixed: 456500
Change-Id: Ibe931251b6f06c6acbe6bc8a095b0e925dc08857
Signed-off-by: Rajeshwar Kurapaty <rkurapat@codeaurora.org>