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/gpio/tegra_gpio.c b/drivers/gpio/tegra_gpio.c
index 5a03115..b01968a 100644
--- a/drivers/gpio/tegra_gpio.c
+++ b/drivers/gpio/tegra_gpio.c
@@ -337,7 +337,8 @@
 	 * This driver does not make use of interrupts, other than to figure
 	 * out the number of GPIO banks
 	 */
-	if (!fdt_getprop(gd->fdt_blob, parent->of_offset, "interrupts", &len))
+	if (!fdt_getprop(gd->fdt_blob, dev_of_offset(parent), "interrupts",
+			 &len))
 		return -EINVAL;
 	bank_count = len / 3 / sizeof(u32);
 	ctlr = (struct gpio_ctlr *)dev_get_addr(parent);
@@ -363,7 +364,7 @@
 					  plat->port_name, plat, -1, &dev);
 			if (ret)
 				return ret;
-			dev->of_offset = parent->of_offset;
+			dev_set_of_offset(dev, dev_of_offset(parent));
 		}
 	}