dm: Use an explicit expect value in core tests

Rather than reusing the 'reg' property, use an explicit property for the
expected ping value used in testing.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/test-fdt.c b/test/dm/test-fdt.c
index 98e3936..0f50537 100644
--- a/test/dm/test-fdt.c
+++ b/test/dm/test-fdt.c
@@ -39,7 +39,8 @@
 
 	pdata->ping_add = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
 					"ping-add", -1);
-	pdata->base = fdtdec_get_addr(gd->fdt_blob, dev->of_offset, "reg");
+	pdata->base = fdtdec_get_addr(gd->fdt_blob, dev->of_offset,
+				      "ping-expect");
 
 	return 0;
 }
@@ -127,11 +128,13 @@
 		ut_assert(!ret);
 
 		/*
-		 * Get the 'reg' property, which tells us what the ping add
-		 * should be. We don't use the platdata because we want
-		 * to test the code that sets that up (testfdt_drv_probe()).
+		 * Get the 'ping-expect' property, which tells us what the
+		 * ping add should be. We don't use the platdata because we
+		 * want to test the code that sets that up
+		 * (testfdt_drv_probe()).
 		 */
-		base = fdtdec_get_addr(gd->fdt_blob, dev->of_offset, "reg");
+		base = fdtdec_get_addr(gd->fdt_blob, dev->of_offset,
+				       "ping-expect");
 		debug("dev=%d, base=%d: %s\n", i, base,
 		      fdt_get_name(gd->fdt_blob, dev->of_offset, NULL));