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/net/sun8i_emac.c b/drivers/net/sun8i_emac.c
index abd9cc8..b87210b 100644
--- a/drivers/net/sun8i_emac.c
+++ b/drivers/net/sun8i_emac.c
@@ -442,7 +442,7 @@
 	const char *pin_name;
 	int drive, pull, i;
 
-	offset = fdtdec_lookup_phandle(gd->fdt_blob, dev->of_offset,
+	offset = fdtdec_lookup_phandle(gd->fdt_blob, dev_of_offset(dev),
 				       "pinctrl-0");
 	if (offset < 0) {
 		printf("WARNING: emac: cannot find pinctrl-0 node\n");
@@ -716,6 +716,7 @@
 	struct eth_pdata *pdata = dev_get_platdata(dev);
 	struct emac_eth_dev *priv = dev_get_priv(dev);
 	const char *phy_mode;
+	int node = dev_of_offset(dev);
 	int offset = 0;
 
 	pdata->iobase = dev_get_addr_name(dev, "emac");
@@ -725,13 +726,13 @@
 	priv->phyaddr = -1;
 	priv->use_internal_phy = false;
 
-	offset = fdtdec_lookup_phandle(gd->fdt_blob, dev->of_offset,
+	offset = fdtdec_lookup_phandle(gd->fdt_blob, node,
 				       "phy");
 	if (offset > 0)
 		priv->phyaddr = fdtdec_get_int(gd->fdt_blob, offset, "reg",
 					       -1);
 
-	phy_mode = fdt_getprop(gd->fdt_blob, dev->of_offset, "phy-mode", NULL);
+	phy_mode = fdt_getprop(gd->fdt_blob, node, "phy-mode", NULL);
 
 	if (phy_mode)
 		pdata->phy_interface = phy_get_interface_by_name(phy_mode);
@@ -751,7 +752,7 @@
 	}
 
 	if (priv->variant == H3_EMAC) {
-		if (fdt_getprop(gd->fdt_blob, dev->of_offset,
+		if (fdt_getprop(gd->fdt_blob, node,
 				"allwinner,use-internal-phy", NULL))
 			priv->use_internal_phy = true;
 	}