msm: vidc: avoid usage of output_tag to get session_id

The firmware will send session_id as part of
struct hfi_msg_event_notify_packet. The driver should use
the session_id in this structure rather than from output_tag.
Without this change release reference event will not
be handled correctly by driver.

Change-Id: I6005482a1b2dfefb6acf0ff797c291197791ca4a
Signed-off-by: Arun Menon <avmenon@codeaurora.org>