drm/radeon/kms: set family for use in parser.

Wierdly the kms parser never initialised the family, it wasn't really used
much, but the fmt checker patch started using it and it fell over.

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>