nv50,nvc0: fix 3d blit logic for odd depth/stencil formats

Reported-by: David Heidelberger <david.heidelberger@ixit.cz>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.2 10.3" <mesa-stable@lists.freedesktop.org>