media: cx88: Get rid of spurious call to cx8800_start_vbi_dma()

This was left over from the conversion to VB2, where the call was
getting invoked both in buffer_queue and start_streaming, which
was intermittently causing invalid opcodes on the VBI RISC queue.

This change effectively mirrors the exact same change Hans Verkuil
made in cx88-video.c in commit 389208e1 ("[media] cx88:
remove leftover start_video_dma() call").

Thanks to Daniel Glöckner for spotting the actual bug after I spent
several days trying to chase down the issue.

Fixes: 389208e1 ("[media] cx88: remove leftover start_video_dma() call")

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Thanks-to: Daniel Glöckner <daniel-gl@gmx.net>
Cc: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>