media: doc-rst: Fix broken references

Documentation and code was linking the old documentation at:
http://v4l2spec.bytesex.org/spec/x1904.htm

Signed-off-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
Signed-off-by: Hans Verkuil <hansverk@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>