media: staging: media: zoran: fix various V4L2 compliance errors

This fixes several issues found with 'v4l2-compliance -s':

1) read()/write() is supported, but not reported in the capabilities
2) S_STD(G_STD()) failed: setting the same standard should just return 0.
3) G_PARM failed to set readbuffers.
4) different field values in the format vs. what v4l2_buffer reported.
5) zero the sequence number when starting streaming.
6) drop VB_USERPTR: makes no sense with dma_contig streaming.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>