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/ram/stm32_sdram.c b/drivers/ram/stm32_sdram.c
index 48b4979..b640519 100644
--- a/drivers/ram/stm32_sdram.c
+++ b/drivers/ram/stm32_sdram.c
@@ -104,7 +104,7 @@
 static int stm32_fmc_ofdata_to_platdata(struct udevice *dev)
 {
 	int ret;
-	int node = dev->of_offset;
+	int node = dev_of_offset(dev);
 	const void *blob = gd->fdt_blob;
 	struct stm32_sdram_params *params = dev_get_platdata(dev);