nv50,nvc0: make sure to pushbuf_refn before putting bo into pushbuf_data

nv50,nvc0: make sure to pushbuf_refn before putting bo into pushbuf_data

Without first running the bo through pushbuf_refn, the nouveau drm
library will have uninitialized structures regarding this bo, and will
insert incorrect data.

This fixes supertuxkart 0.9 crash on start (where it ends up doing a lot
of indirect draws).

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>