i965/fs: Don't mess up stride for uniform integer multiplication.
If the stride is 0, the source is a uniform and we should not modify the stride. Cc: "10.6" <mesa-stable@lists.freedesktop.org> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91047 Reviewed-by:Kenneth Graunke <kenneth@whitecape.org> (cherry picked from commit a49328d5)