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/usb/musb-new/pic32.c b/drivers/usb/musb-new/pic32.c
index c888c64..ed6da19 100644
--- a/drivers/usb/musb-new/pic32.c
+++ b/drivers/usb/musb-new/pic32.c
@@ -219,7 +219,7 @@
 	struct musb_host_data *mdata = &pdata->mdata;
 	struct fdt_resource mc, glue;
 	void *fdt = (void *)gd->fdt_blob;
-	int node = dev->of_offset;
+	int node = dev_of_offset(dev);
 	void __iomem *mregs;
 	int ret;