drm/usb: bind driver to correct device

commit 9f23de52b64f7fb801fd76f3dd8651a0dc89187b upstream.

While looking at plymouth on udl I noticed that plymouth was trying
to use its fb plugin not its drm one, it was trying to drmOpen a driver called
usb not udl, noticed that we actually had out driver pointing at the wrong
device.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>