nouveau: when mapping a persistent buffer, synchronize on former xfers

If the buffer is being used, we should wait for those uses to be
complete before returning the map.

Fixes: GL45-CTS.direct_state_access.buffers_functional
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: mesa-stable@lists.freedesktop.org
(cherry picked from commit d9cc58d6ec56e676b1285508a4118a83f5325833)
1 file changed