[media] coda: remove unused isequence, reset qsequence in stop_streaming

The isequence counter is never used, qsequence counts the buffers queued into
the bit decoder bitstream ringbuffer. It needs to be reset in stop_streaming.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>