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/arm/mach-aspeed/ast2500/sdram_ast2500.c b/arch/arm/mach-aspeed/ast2500/sdram_ast2500.c
index ace1028..cb6e03f 100644
--- a/arch/arm/mach-aspeed/ast2500/sdram_ast2500.c
+++ b/arch/arm/mach-aspeed/ast2500/sdram_ast2500.c
@@ -392,7 +392,7 @@
 	priv->regs = regmap_get_range(map, 0);
 	priv->phy = regmap_get_range(map, 1);
 
-	priv->clock_rate = fdtdec_get_int(gd->fdt_blob, dev->of_offset,
+	priv->clock_rate = fdtdec_get_int(gd->fdt_blob, dev_of_offset(dev),
 					  "clock-frequency", 0);
 
 	if (!priv->clock_rate) {
diff --git a/arch/arm/mach-rockchip/rk3288/sdram_rk3288.c b/arch/arm/mach-rockchip/rk3288/sdram_rk3288.c
index be3d713..89fd8e6 100644
--- a/arch/arm/mach-rockchip/rk3288/sdram_rk3288.c
+++ b/arch/arm/mach-rockchip/rk3288/sdram_rk3288.c
@@ -1016,7 +1016,7 @@
 #if !CONFIG_IS_ENABLED(OF_PLATDATA)
 	struct rk3288_sdram_params *params = dev_get_platdata(dev);
 	const void *blob = gd->fdt_blob;
-	int node = dev->of_offset;
+	int node = dev_of_offset(dev);
 	int ret;
 
 	/* Rk3288 supports dual-channel, set default channel num to 2 */