ARM: dts: vfxxx: Pass 'mmc' as the esdhc node names

Pass 'mmc' as the esdhc node names to fix the following schema
warnings:

vf610-cosmic.dtb: esdhc@400b1000: $nodename:0: 'esdhc@400b1000' does not match '^mmc(@.*)?$'
Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/nxp/vf/vfxxx.dtsi

@@ -569,7 +569,7 @@ adc1: adc@400bb000 {
 							<20000000>;
 			};
 
-			esdhc0: esdhc@400b1000 {
+			esdhc0: mmc@400b1000 {
 				compatible = "fsl,imx53-esdhc";
 				reg = <0x400b1000 0x1000>;
 				interrupts = <27 IRQ_TYPE_LEVEL_HIGH>;
@@ -580,7 +580,7 @@ esdhc0: esdhc@400b1000 {
 				status = "disabled";
 			};
 
-			esdhc1: esdhc@400b2000 {
+			esdhc1: mmc@400b2000 {
 				compatible = "fsl,imx53-esdhc";
 				reg = <0x400b2000 0x1000>;
 				interrupts = <28 IRQ_TYPE_LEVEL_HIGH>;