cmd/compile/internal/test: fix typo in comments

Change-Id: Iba6bb7f8252120f56d7e6ae49c9edc9382e8c7e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/679855
Reviewed-by: abner chenc <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Mark Freeman <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: sophie-zhao

src/cmd/compile/internal/test/mulconst_test.go

@@ -143,7 +143,7 @@ func BenchmarkMulconstI32(b *testing.B) {
 		}
 		mulSinkI32 = x
 	})
-	// -120x = 8x - 120x
+	// -120x = 8x - 128x
 	b.Run("-120", func(b *testing.B) {
 		x := int32(1)
 		for i := 0; i < b.N; i++ {
@@ -202,7 +202,7 @@ func BenchmarkMulconstI64(b *testing.B) {
 		}
 		mulSinkI64 = x
 	})
-	// -120x = 8x - 120x
+	// -120x = 8x - 128x
 	b.Run("-120", func(b *testing.B) {
 		x := int64(1)
 		for i := 0; i < b.N; i++ {