cmd/compile/internal/ssa: fix spelling mistake

Change-Id: I4b8f1b61c10f60ddb3687759af0be1641c1f78ce
Reviewed-on: https://go-review.googlesource.com/43111Reviewed-by: Alex Brainman <alex.brainman@gmail.com>

src/cmd/compile/internal/ssa/cse.go

@@ -322,7 +322,7 @@ func cmpVal(v, w *Value, auxIDs auxmap) types.Cmp {
 		// that generate memory.
 		return lt2Cmp(v.ID < w.ID)
 	}
-	// OpSelect is a pseudo-op. We need to be more agressive
+	// OpSelect is a pseudo-op. We need to be more aggressive
 	// regarding CSE to keep multiple OpSelect's of the same
 	// argument from existing.
 	if v.Op != OpSelect0 && v.Op != OpSelect1 {