[media] go7007: drop struct go7007_file

Remove struct go7007_file: all fields contained in that struct are moved to
the go7007 struct since they are really global values. The lock has just
been deleted (what's the point of a per-fh lock??).

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