doc: device-tree-bindings: update reference to binding directory

Update reference in files detected by
scripts/documentation-file-ref-check

doc/devicetree/device-tree-bindings/  => doc/device-tree-bindings/
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>

doc/device-tree-bindings/video/rockchip-lvds.txt

@@ -20,7 +20,7 @@ Required properties:
 	<LVDS_OUTPUT_DUAL>, This describes the output face.
 
 - display-timings : described by
-	doc/devicetree/device-tree-bindings/video/display-timing.txt.
+	doc/device-tree-bindings/video/display-timing.txt.
 
 Example:
 	lvds: lvds@ff96c000 {