[media] em28xx: fix VIDIOC_DBG_G_CHIP_IDENT compliance errors

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