dm: core: Add ofnode_for_each_subnode()

Add a convenience macro to iterate over subnodes of a node. Make use of
this where appropriate in the code.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/ofnode.c b/drivers/core/ofnode.c
index 0685b68..c6ca13f 100644
--- a/drivers/core/ofnode.c
+++ b/drivers/core/ofnode.c
@@ -390,10 +390,11 @@
 	if (!ofnode_valid(timings))
 		return -EINVAL;
 
-	for (i = 0, node = ofnode_first_subnode(timings);
-	     ofnode_valid(node) && i != index;
-	     node = ofnode_first_subnode(node))
-		i++;
+	i = 0;
+	ofnode_for_each_subnode(node, timings) {
+		if (i++ == index)
+			break;
+	}
 
 	if (!ofnode_valid(node))
 		return -EINVAL;
diff --git a/drivers/misc/cros_ec.c b/drivers/misc/cros_ec.c
index feaa5d8..eefaaa5 100644
--- a/drivers/misc/cros_ec.c
+++ b/drivers/misc/cros_ec.c
@@ -1038,8 +1038,7 @@
 
 	config->flash_erase_value = ofnode_read_s32_default(flash_node,
 							    "erase-value", -1);
-	for (node = ofnode_first_subnode(flash_node); ofnode_valid(node);
-	     node = ofnode_next_subnode(node)) {
+	ofnode_for_each_subnode(node, flash_node) {
 		const char *name = ofnode_get_name(node);
 		enum ec_flash_region region;
 
diff --git a/drivers/power/pmic/pmic-uclass.c b/drivers/power/pmic/pmic-uclass.c
index 953bbe5..64964e4 100644
--- a/drivers/power/pmic/pmic-uclass.c
+++ b/drivers/power/pmic/pmic-uclass.c
@@ -34,9 +34,7 @@
 	debug("%s for '%s' at node offset: %d\n", __func__, pmic->name,
 	      dev_of_offset(pmic));
 
-	for (node = ofnode_first_subnode(parent);
-	     ofnode_valid(node);
-	     node = ofnode_next_subnode(node)) {
+	ofnode_for_each_subnode(node, parent) {
 		node_name = ofnode_get_name(node);
 
 		debug("* Found child node: '%s'\n", node_name);