[media] s2255: don't zero struct v4l2_streamparm

All fields after 'type' are already zeroed by the core framework.
Clearing the full struct also clears 'type', which causes a wrong
type value to be returned.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>