dm: core: Access device ofnode through functions

At present ofnode is present in the device even if it is never used. With
of-platdata this field is not used, so can be removed. In preparation for
this, change the access to go through inline functions.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/video/rockchip/rk_mipi.c b/drivers/video/rockchip/rk_mipi.c
index d125a5b..159201a 100644
--- a/drivers/video/rockchip/rk_mipi.c
+++ b/drivers/video/rockchip/rk_mipi.c
@@ -119,7 +119,7 @@
 	rk_mipi_dsi_write(regs, VID_PKT_SIZE, 0x4b0);
 
 	/* Set dpi color coding depth 24 bit */
-	timing_node = ofnode_find_subnode(dev->node, "display-timings");
+	timing_node = ofnode_find_subnode(dev_ofnode(dev), "display-timings");
 	node = ofnode_first_subnode(timing_node);
 
 	val = ofnode_read_u32_default(node, "bits-per-pixel", -1);