dm: core: Test uclass_first/next_device() on probe failure

Add some tests which check the behaviour of uclass_first_device() and
uclass_next_device() when probing of a device fails.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/dts/test.dts b/arch/sandbox/dts/test.dts
index 7dde95d..65b2f8e 100644
--- a/arch/sandbox/dts/test.dts
+++ b/arch/sandbox/dts/test.dts
@@ -289,6 +289,25 @@
 		};
 	};
 
+	probing {
+		compatible = "simple-bus";
+		test1 {
+			compatible = "denx,u-boot-probe-test";
+		};
+
+		test2 {
+			compatible = "denx,u-boot-probe-test";
+		};
+
+		test3 {
+			compatible = "denx,u-boot-probe-test";
+		};
+
+		test4 {
+			compatible = "denx,u-boot-probe-test";
+		};
+	};
+
 	pwrdom: power-domain {
 		compatible = "sandbox,power-domain";
 		#power-domain-cells = <1>;