media: dvb: Fix TS buffer insertion

Openning the insertion source used an invalid pointer for
the relevant mpq_demux object. Also, reference count was
not decremented properly when detaching the insertion pipe.

Change-Id: Ifea627ee55cc2af34d2e3fc72d164ba794791768
Signed-off-by: Gilad Broner <gbroner@codeaurora.org>