st/nine: Ignore nooverwrite for systemmem

Systemmem has a specific behaviour we don't
mimick exactly.
That makes Halo feel free to use nooverwrite
with it all the time, even when reading again
at the same location.
Ignore nooverwrite to have proper synchronization.

Fixes: https://github.com/iXit/Mesa-3D/issues/348

Signed-off-by: Axel Davy <davyaxel0@gmail.com>

src/gallium/state_trackers/nine/buffer9.c

@@ -276,7 +276,7 @@ NineBuffer9_Lock( struct NineBuffer9 *This,
      * Our tests: SYSTEMMEM doesn't DISCARD */
 
     if (This->base.pool == D3DPOOL_SYSTEMMEM)
-        Flags &= ~D3DLOCK_DISCARD;
+        Flags &= ~(D3DLOCK_DISCARD | D3DLOCK_NOOVERWRITE);
 
     if (Flags & D3DLOCK_DISCARD)
         usage = PIPE_TRANSFER_WRITE | PIPE_TRANSFER_DISCARD_WHOLE_RESOURCE;