ARM: dts: imx6qdl-apalis: Add a label for the touchscreen

Add a label for the touchscreen to allow a custom baseboard to
disable this node if needed.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6qdl-apalis.dtsi

@@ -313,7 +313,7 @@ stmpe811@41 {
 		/* ADC converstion time: 80 clocks */
 		st,sample-time = <4>;
 
-		stmpe-touchscreen {
+		stmpe_touchscreen: stmpe-touchscreen {
 			compatible = "st,stmpe-ts";
 			/* 8 sample average control */
 			st,ave-ctrl = <3>;