media: staging/intel-ipu3: Reset imgu_video_device sequence

Reset the sequence number of imgu_video_device on stream start.
Failing to do so results in sequence number getting incremented
for consecutive stream on/off cycles.

Signed-off-by: Umang Jain <umang.jain@ideasonboard.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>