[media] v4l2-framework: replace g_chip_ident by g_std in the examples

The framework documentation used the g_chip_ident op as an example. This
op has been removed, so replace its use in the examples by the g_std op.

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