dt-bindings: fsl-imx-drm: Remove incorrect "@di0" usage

Improve the binding example by removing the '@di0' notation, which
fixes the following build warning:

Warning (unit_address_vs_reg): Node /display@di0 has a unit name, but
no reg property
Signed-off-by: NMarco Franchi <marco.franchi@nxp.com>
Signed-off-by: NPhilipp Zabel <p.zabel@pengutronix.de>

Documentation/devicetree/bindings/display/imx/fsl-imx-drm.txt

@@ -129,7 +129,7 @@ Optional properties:
 
 example:
 
-display@di0 {
+disp0 {
 	compatible = "fsl,imx-parallel-display";
 	edid = [edid-data];
 	interface-pix-fmt = "rgb24";