ARM: dts: use 'atmel' as at24 manufacturer in am335x-boneblue

Using 'at' as the <manufacturer> part of the compatible string is now
deprecated. Use a correct string: 'atmel,<model>'.

Signed-off-by: Bartosz Golaszewski <[e-mail]>
Signed-off-by: Tony Lindgren <[e-mail]>

arch/arm/boot/dts/am335x-boneblue.dts

···
 	};
 
 	baseboard_eeprom: baseboard_eeprom@50 {
-		compatible = "at,24c256";
+		compatible = "atmel,24c256";
 		reg = <0x50>;
 
 		#address-cells = <1>;