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: Sylvain Lemieux <slemieux.tyco@gmail.com>
Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>