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/intel_broadwell_gpio.c b/drivers/gpio/intel_broadwell_gpio.c
index 81ce446..790577a 100644
--- a/drivers/gpio/intel_broadwell_gpio.c
+++ b/drivers/gpio/intel_broadwell_gpio.c
@@ -149,14 +149,14 @@
 	if (ret)
 		return ret;
 
-	bank = fdtdec_get_int(gd->fdt_blob, dev->of_offset, "reg", -1);
+	bank = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev), "reg", -1);
 	if (bank == -1) {
 		debug("%s: Invalid bank number %d\n", __func__, bank);
 		return -EINVAL;
 	}
 	plat->bank = bank;
 	plat->base_addr = gpiobase;
-	plat->bank_name = fdt_getprop(gd->fdt_blob, dev->of_offset,
+	plat->bank_name = fdt_getprop(gd->fdt_blob, dev_of_offset(dev),
 				      "bank-name", NULL);
 
 	return 0;