V4L/DVB: ivtv: Add delay to ensure the decoder always restarts with a blank screen

Add a short delay when stopping the decoder, allowing it to settle and
preventing some unexpected interaction with other firmware commands.

Signed-off-by: Ian Armstrong <ian@iarmst.demon.co.uk>
Tested-by: Martin Dauskardt <martin.dauskardt@gmx.de>
Signed-off-by: Andy Walls <awalls@md.metrocast.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>