media: venus: destroy hfi session after m2m_ctx release

This partially reverts commit that made hfi_session_destroy()
the first step of vdec/venc close().  The reason being is a
regression report when, supposedly, encode/decoder is closed
with still active streaming (no ->stop_streaming() call before
close()) and pending pkts, so isr_thread cannot find instance
and fails to process those pending pkts.  This was the idea
behind the original patch - make it impossible to use instance
under destruction, because this is racy, but apparently there
are uses cases that depend on that unsafe pattern.  Return to
the old (unsafe) behaviour for the time being (until a better
fix is found).

Fixes: 45b1a1b3 ("media: venus: sync with threaded IRQ during inst destruction")
Cc: stable@vger.kernel.org
Reported-by: Nathan Hebert <nhebert@google.com>
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Signed-off-by: Stanimir Varbanov <stanimir.k.varbanov@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>