runtime: add space

Missed this in review of 20812

Change-Id: I01e220499dcd58e1a7205e2a577dd9630a8b7174
Reviewed-on: https://go-review.googlesource.com/20819
Reviewed-by: Keith Randall <khr@golang.org>

src/runtime/hash_test.go

@@ -671,6 +671,7 @@ func BenchmarkAlignedLoad(b *testing.B) {
 	}
 	sink = s
 }
+
 func BenchmarkUnalignedLoad(b *testing.B) {
 	var buf [16]byte
 	p := unsafe.Pointer(&buf[1])