virtio: convert bus code to use dev_groups
virtio: convert bus code to use dev_groups

The dev_attrs field of struct bus_type is going away soon, dev_groups
should be used instead.  This converts the virtio bus code to use the
correct field.

Cc: Rusty Russell <df9728c9e5104131c08c7adb03af425394842596@rustcorp.com.au>
Cc: "Michael S. Tsirkin" <255103e50249e3d658441816e0597170ebfc16ef@redhat.com>
Cc: <65ac89e807f0ba8b231fca45370e2e73a1754d6e@lists.linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <4645f7897fd33786a2ee1264d590b3c400559d85@linuxfoundation.org>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs