nvc0/ir: avoid infinite recursion when finding first uses of tex

nvc0/ir: avoid infinite recursion when finding first uses of tex

In certain circumstances, findFirstUses could end up doubling back on
instructions it had already processed, resulting in an infinite
recursion. Avoid this by keeping track of already-visited instructions.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=83079
Tested-by: Tobias Klausmann <tobias.johannes.klausmann@mni.thm.de>
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "10.2 10.3" <mesa-stable@lists.freedesktop.org>