ARM: dts: lpc32xx: ea3250: fix Atmel at24 eeprom vendor

There is no 'at' hardware vendor defined yet, correct vendor prefix
for Atmel is 'atmel'.
Acked-by: NSylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: NVladimir Zapolskiy <vz@mleia.com>

arch/arm/boot/dts/ea3250.dts

@@ -162,12 +162,12 @@
 	};
 
 	eeprom@50 {
-		compatible = "at,24c256";
+		compatible = "atmel,24c256";
 		reg = <0x50>;
 	};
 
 	eeprom@57 {
-		compatible = "at,24c64";
+		compatible = "atmel,24c64";
 		reg = <0x57>;
 	};