ARM: dts: imx6ull: use same compatible string as Linux is using

The GPMI NAND IP seems to be the same as used in i.MX 6Quad. Use
the fsl,imx6q-gpmi-nand compatible string like Linux devices trees
are.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>

arch/arm/dts/imx6ull.dtsi

@@ -190,7 +190,7 @@
 		};
 
 		gpmi: gpmi-nand@01806000{
-			compatible = "fsl,imx6ull-gpmi-nand", "fsl, imx6ul-gpmi-nand";
+			compatible = "fsl,imx6q-gpmi-nand";
 			#address-cells = <1>;
 			#size-cells = <1>;
 			reg = <0x01806000 0x2000>, <0x01808000 0x4000>;