r600: fix constant buffer bounds.

r600: fix constant buffer bounds.

If you have an indirect access to a constant buffer on r600/eg
use a vertex fetch in the shader. However apps have expected
behaviour on those out of bounds accessess (even if illegal).

If the constants were being uploaded as part of a larger
upload buffer, we'd set the range of allowed access to a lot
larger than required so apps would get values back from
other parts of the upload buffer instead of the expected out
of bounds access.

This fixes rendering bugs in Trine and Witcher 1, thanks
to iive for nagging me effectively until I figured it out :-)

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91808
Cc: <mesa-stable@lists.freedesktop.org>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>