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/pinctrl/pinctrl-at91.c b/drivers/pinctrl/pinctrl-at91.c
index 023cc01..38c435e 100644
--- a/drivers/pinctrl/pinctrl-at91.c
+++ b/drivers/pinctrl/pinctrl-at91.c
@@ -364,7 +364,7 @@
 {
 	struct at91_pinctrl_priv *priv = dev_get_priv(dev);
 	const void *blob = gd->fdt_blob;
-	int node = config->of_offset;
+	int node = dev_of_offset(config);
 	u32 cells[MAX_PINMUX_ENTRIES];
 	const u32 *list = cells;
 	u32 bank, pin;