gallium/hud: do not specify potentially invalid depth-range

gallium/hud: do not specify potentially invalid depth-range

Setting the depth-scale to 1 while leaving the depth-translation at 0
means our near-plane is at -1 in OpenGL semantics, which is
out-of-range on some drivers. In particular, Zink has this limitation.

But since we'll only pass a zero z in here anyway, we might as well
multiply it by zero, and get the same result. This avoids the problem.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5408>