msm: vidc: On session_end_done only free current session context

Currently, the msm_vidc driver is freeing the contexts of all the active
sessions, causing hanging pointers and general memory corruption.  We
should only be closing the context of the session that is ending.

Change-Id: Ie7bbd5a5b31f79a3ed80bca84b4ec0cc7e6bb013
CRs-Fixed: 407718
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>