dm: core: Replace of_offset with accessor (part 2)

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/phy/ti-pipe3-phy.c b/drivers/phy/ti-pipe3-phy.c
index 350dab7..680e32f 100644
--- a/drivers/phy/ti-pipe3-phy.c
+++ b/drivers/phy/ti-pipe3-phy.c
@@ -296,7 +296,7 @@
 		return NULL;
 	}
 
-	cell = fdt_getprop(gd->fdt_blob, dev->of_offset, name,
+	cell = fdt_getprop(gd->fdt_blob, dev_of_offset(dev), name,
 			   &len);
 	if (len < 2*sizeof(fdt32_t)) {
 		error("offset not available for %s\n", name);