[dev.ssa] cmd/compile/ssa: fix test for dse

Fix the test broken with dee1f2 by implementing Elem()

Change-Id: I7a4a487885267c24fdc52d79fb7d450231328812
Reviewed-on: https://go-review.googlesource.com/13551
Reviewed-by: Keith Randall <khr@golang.org>
diff --git a/src/cmd/compile/internal/ssa/deadstore_test.go b/src/cmd/compile/internal/ssa/deadstore_test.go
index 8d9b4b1..634192f 100644
--- a/src/cmd/compile/internal/ssa/deadstore_test.go
+++ b/src/cmd/compile/internal/ssa/deadstore_test.go
@@ -8,7 +8,8 @@
 
 func TestDeadStore(t *testing.T) {
 	c := testConfig(t)
-	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr"} // dummy for testing
+	elemType := &TypeImpl{Size_: 8, Name: "testtype"}
+	ptrType := &TypeImpl{Size_: 8, Ptr: true, Name: "testptr", Elem_: elemType} // dummy for testing
 	fun := Fun(c, "entry",
 		Bloc("entry",
 			Valu("start", OpArg, TypeMem, 0, ".mem"),