drm/i915: Fix misleading driver debug message

Stop claiming that UMS support is disabled when it's not actually
supported anymore.

Signed-off-by: Frank Binns <frank.binns@imgtec.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1466763836-27772-1-git-send-email-frank.binns@imgtec.com
Link: http://patchwork.freedesktop.org/patch/msgid/1466773227-7994-13-git-send-email-chris@chris-wilson.co.uk