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/clk/at91/clk-generated.c b/drivers/clk/at91/clk-generated.c
index d36f64f..ac27d3e 100644
--- a/drivers/clk/at91/clk-generated.c
+++ b/drivers/clk/at91/clk-generated.c
@@ -154,9 +154,8 @@
 	u32 num_parents;
 
 	num_parents = fdtdec_get_int_array_count(gd->fdt_blob,
-						 dev_get_parent(dev)->of_offset,
-						 "clocks", cells,
-						 GENERATED_SOURCE_MAX);
+			dev_of_offset(dev_get_parent(dev)), "clocks", cells,
+			GENERATED_SOURCE_MAX);
 
 	if (!num_parents)
 		return -1;
diff --git a/drivers/clk/at91/pmc.c b/drivers/clk/at91/pmc.c
index 76ba91a..c73156a 100644
--- a/drivers/clk/at91/pmc.c
+++ b/drivers/clk/at91/pmc.c
@@ -47,7 +47,7 @@
 int at91_clk_sub_device_bind(struct udevice *dev, const char *drv_name)
 {
 	const void *fdt = gd->fdt_blob;
-	int offset = dev->of_offset;
+	int offset = dev_of_offset(dev);
 	bool pre_reloc_only = !(gd->flags & GD_FLG_RELOC);
 	const char *name;
 	int ret;
@@ -90,7 +90,8 @@
 		return -EINVAL;
 	}
 
-	periph = fdtdec_get_uint(gd->fdt_blob, clk->dev->of_offset, "reg", -1);
+	periph = fdtdec_get_uint(gd->fdt_blob, dev_of_offset(clk->dev), "reg",
+				 -1);
 	if (periph < 0)
 		return -EINVAL;