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/pinctrl/rockchip/pinctrl_rk3036.c b/drivers/pinctrl/rockchip/pinctrl_rk3036.c
index 6aea856..8d42584 100644
--- a/drivers/pinctrl/rockchip/pinctrl_rk3036.c
+++ b/drivers/pinctrl/rockchip/pinctrl_rk3036.c
@@ -205,7 +205,7 @@
 	u32 cell[3];
 	int ret;
 
-	ret = fdtdec_get_int_array(gd->fdt_blob, periph->of_offset,
+	ret = fdtdec_get_int_array(gd->fdt_blob, dev_of_offset(periph),
 				   "interrupts", cell, ARRAY_SIZE(cell));
 	if (ret < 0)
 		return -EINVAL;