dm: core: Replace of_offset with accessor

At present devices use a simple integer offset to record the device tree
node associated with the device. In preparation for supporting a live
device tree, which uses a node pointer instead, refactor existing code to
access this field through an inline function.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/core/uclass.c b/drivers/core/uclass.c
index 60610e5..7de3706 100644
--- a/drivers/core/uclass.c
+++ b/drivers/core/uclass.c
@@ -278,7 +278,7 @@
 		return ret;
 
 	list_for_each_entry(dev, &uc->dev_head, uclass_node) {
-		if (dev->of_offset == node) {
+		if (dev_of_offset(dev) == node) {
 			*devp = dev;
 			return 0;
 		}
@@ -299,7 +299,7 @@
 	int ret;
 
 	*devp = NULL;
-	find_phandle = fdtdec_get_int(gd->fdt_blob, parent->of_offset, name,
+	find_phandle = fdtdec_get_int(gd->fdt_blob, dev_of_offset(parent), name,
 				      -1);
 	if (find_phandle <= 0)
 		return -ENOENT;
@@ -308,7 +308,9 @@
 		return ret;
 
 	list_for_each_entry(dev, &uc->dev_head, uclass_node) {
-		uint phandle = fdt_get_phandle(gd->fdt_blob, dev->of_offset);
+		uint phandle;
+
+		phandle = fdt_get_phandle(gd->fdt_blob, dev_of_offset(dev));
 
 		if (phandle == find_phandle) {
 			*devp = dev;