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/i2c/muxes/i2c-arb-gpio-challenge.c b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
index 3f072c7..66ce7ec 100644
--- a/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
+++ b/drivers/i2c/muxes/i2c-arb-gpio-challenge.c
@@ -89,7 +89,7 @@
 {
 	struct i2c_arbitrator_priv *priv = dev_get_priv(dev);
 	const void *blob = gd->fdt_blob;
-	int node = dev->of_offset;
+	int node = dev_of_offset(dev);
 	int ret;
 
 	debug("%s: %s\n", __func__, dev->name);
diff --git a/drivers/i2c/muxes/i2c-mux-uclass.c b/drivers/i2c/muxes/i2c-mux-uclass.c
index db086ef..d243b8e 100644
--- a/drivers/i2c/muxes/i2c-mux-uclass.c
+++ b/drivers/i2c/muxes/i2c-mux-uclass.c
@@ -40,7 +40,7 @@
 	struct i2c_mux_bus *plat = dev_get_parent_platdata(dev);
 	int channel;
 
-	channel = fdtdec_get_int(gd->fdt_blob, dev->of_offset, "reg", -1);
+	channel = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev), "reg", -1);
 	if (channel < 0)
 		return -EINVAL;
 	plat->channel = channel;
@@ -60,7 +60,7 @@
 	 * There is no compatible string in the sub-nodes, so we must manually
 	 * bind these
 	 */
-	for (offset = fdt_first_subnode(blob, mux->of_offset);
+	for (offset = fdt_first_subnode(blob, dev_of_offset(mux));
 	     offset > 0;
 	     offset = fdt_next_subnode(blob, offset)) {
 		struct udevice *dev;
diff --git a/drivers/i2c/muxes/pca954x.c b/drivers/i2c/muxes/pca954x.c
index 7e0d2da..1a67618 100644
--- a/drivers/i2c/muxes/pca954x.c
+++ b/drivers/i2c/muxes/pca954x.c
@@ -51,7 +51,7 @@
 {
 	struct pca954x_priv *priv = dev_get_priv(dev);
 
-	priv->addr = fdtdec_get_int(gd->fdt_blob, dev->of_offset, "reg", 0);
+	priv->addr = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev), "reg", 0);
 	if (!priv->addr) {
 		debug("MUX not found\n");
 		return -ENODEV;