nv50/ir: delete MINMAX instruction that is no longer in the BB

We removed the op from the BB, but it was still listed in its sources'
uses. This could trip up some logic down the line which analyzes all the
uses of an l-value, e.g. spilling.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Karol Herbst <kherbst@redhat.com>

src/gallium/drivers/nouveau/codegen/nv50_ir_peephole.cpp

@@ -1898,7 +1898,7 @@ AlgebraicOpt::handleMINMAX(Instruction *minmax)
    if (minmax->src(0).mod == minmax->src(1).mod) {
       if (minmax->def(0).mayReplace(minmax->src(0))) {
          minmax->def(0).replace(minmax->src(0), false);
-         minmax->bb->remove(minmax);
+         delete_Instruction(prog, minmax);
       } else {
          minmax->op = OP_CVT;
          minmax->setSrc(1, NULL);