mm-camera2:isp2: Avoid use after free buffer

In the code, there are certain calls that can
try to access the bffer pointer variable after
free, as the same pointer can be freed at
RELEASE_BUF call at the same time.

Change-Id: I4f7a48613b614138916ae33e7783b0c172330321
Signed-off-by: Meera Gande <mgande@codeaurora.org>