[media] saa7164: replace current_norm by g_std

current_norm is deprecated. Replace it by g_std.

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