[media] fsl-viu: remove current_norm

The use of current_norm is deprecated, so remove it. This driver actually
already implements g_std, which overrides current_norm, but the 'std' field
was never initialized correctly. This has been fixed as well.

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