drm/vmwgfx: fix memory corruption with legacy/sou connectors

It looks like in all cases 'struct vmw_connector_state' is used.  But
only in stdu connectors, was atomic_{duplicate,destroy}_state() properly
subclassed.  Leading to writes beyond the end of the allocated connector
state block and all sorts of fun memory corruption related crashes.

Fixes: d7721ca7

 "drm/vmwgfx: Connector atomic state"
Cc: <stable@vger.kernel.org>
Signed-off-by: Rob Clark <rclark@redhat.com>
Reviewed-by: Thomas Hellstrom <thellstrom@vmware.com>