ARM: dts: at91: at91-sama5d27_som1: fix EEPROM compatible

AT24 compatibles require a vendor prefix. Use the default "atmel".

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20201026104618.23415-1-brgl@bgdev.pl