go.tools/go/ssa: add Max to Slice's SSA operand list

LGTM=adonovan
R=adonovan, bradfitz
CC=golang-codereviews
https://golang.org/cl/101160043
diff --git a/go/ssa/ssa.go b/go/ssa/ssa.go
index e68650e..d4d5333 100644
--- a/go/ssa/ssa.go
+++ b/go/ssa/ssa.go
@@ -1655,7 +1655,7 @@
 }
 
 func (v *Slice) Operands(rands []*Value) []*Value {
-	return append(rands, &v.X, &v.Low, &v.High)
+	return append(rands, &v.X, &v.Low, &v.High, &v.Max)
 }
 
 func (s *Store) Operands(rands []*Value) []*Value {