msm: vidc: Do a proper clean-up in case of session abort

A ctrl-c while the venus session is on causes WARN_ON
from function __vb2_queue_cancel. This fix will ensure that
all buffers are returned to vb2 when a stream off is called.
Also there is no need to process release reference event in
the case of session stop.

Change-Id: Id7bf05a17efe237791ad17585d04b59a16bd76d8
Signed-off-by: Praveen Kumar Dwivedi <pkd@codeaurora.org>