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/mmc/sdhci-cadence.c b/drivers/mmc/sdhci-cadence.c
index 4452be0..4bd2623 100644
--- a/drivers/mmc/sdhci-cadence.c
+++ b/drivers/mmc/sdhci-cadence.c
@@ -139,7 +139,7 @@
 	host->ioaddr = plat->hrs_addr + SDHCI_CDNS_SRS_BASE;
 	host->quirks |= SDHCI_QUIRK_WAIT_SEND_CMD;
 
-	ret = sdhci_cdns_phy_init(plat, gd->fdt_blob, dev->of_offset);
+	ret = sdhci_cdns_phy_init(plat, gd->fdt_blob, dev_of_offset(dev));
 	if (ret)
 		return ret;