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/arch/x86/lib/pinctrl_ich6.c b/arch/x86/lib/pinctrl_ich6.c
index fb2d294..406852d 100644
--- a/arch/x86/lib/pinctrl_ich6.c
+++ b/arch/x86/lib/pinctrl_ich6.c
@@ -187,7 +187,7 @@
 		return -EINVAL;
 	}
 
-	for (pin_node = fdt_first_subnode(gd->fdt_blob, dev->of_offset);
+	for (pin_node = fdt_first_subnode(gd->fdt_blob, dev_of_offset(dev));
 	     pin_node > 0;
 	     pin_node = fdt_next_subnode(gd->fdt_blob, pin_node)) {
 		/* Configure the pin */