test: Update tests to use the skip feature

Some tests currently return 0 when they want to be skipped. Update them to
return -EAGAIN instead, so they are counted as skipped.

A few tests are in two parts, with the latter part being skipped in
certain situations. Split these into two and use the correct condition for
the second part.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/dm/of_platdata.c b/test/dm/of_platdata.c
index 7af798b..a241c42 100644
--- a/test/dm/of_platdata.c
+++ b/test/dm/of_platdata.c
@@ -150,7 +150,7 @@
 
 	/* Skip this test if there is no platform data */
 	if (!CONFIG_IS_ENABLED(OF_PLATDATA_DRIVER_RT))
-		return 0;
+		return -EAGAIN;
 
 	/* Record the indexes that are found */
 	memset(found, '\0', sizeof(found));
diff --git a/test/dm/ofnode.c b/test/dm/ofnode.c
index 41811ec..8077aff 100644
--- a/test/dm/ofnode.c
+++ b/test/dm/ofnode.c
@@ -753,10 +753,7 @@
 
 static int dm_test_ofnode_root(struct unit_test_state *uts)
 {
-	char fdt[256];
-	oftree tree;
 	ofnode node;
-	int ret;
 
 	/* Check that aliases work on the control FDT */
 	node = ofnode_get_aliases_node("ethernet3");
@@ -765,14 +762,22 @@
 
 	ut_assert(!oftree_valid(oftree_null()));
 
+	return 0;
+}
+DM_TEST(dm_test_ofnode_root, UT_TESTF_SCAN_FDT);
+
+static int dm_test_ofnode_root_mult(struct unit_test_state *uts)
+{
+	char fdt[256];
+	oftree tree;
+	ofnode node;
+
+	/* skip this test if multiple FDTs are not supported */
+	if (!IS_ENABLED(CONFIG_OFNODE_MULTI_TREE))
+		return -EAGAIN;
+
 	ut_assertok(make_ofnode_fdt(uts, fdt, sizeof(fdt), 0));
-	ret = get_oftree(uts, fdt, &tree);
-
-	/* skip the rest of this test if multiple FDTs are not supported */
-	if (ret == -EOVERFLOW)
-		return 0;
-
-	ut_assertok(ret);
+	ut_assertok(get_oftree(uts, fdt, &tree));
 	ut_assert(oftree_valid(tree));
 
 	/* Make sure they don't work on this new tree */
@@ -791,7 +796,7 @@
 
 	return 0;
 }
-DM_TEST(dm_test_ofnode_root, UT_TESTF_SCAN_FDT);
+DM_TEST(dm_test_ofnode_root_mult, UT_TESTF_SCAN_FDT);
 
 static int dm_test_ofnode_livetree_writing(struct unit_test_state *uts)
 {