drm/ttm: drop man->bdev link.

This link isn't needed anymore, drop it from the init interface.

Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200804025632.3868079-54-airlied@gmail.com