[media] ivtv: remove g_chip_ident

g_chip_ident was used to determine if a saa7114 or saa7115 was used. Instead
just check the subdev name.
After that the g_chip_ident function can be removed.

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