dts: sunxi: correct vendor prefix on OLinuXino a10s micro

The OLinuXino A10S micro features an eeprom. According to the eeprom.txt
binding document, we should use the manufacturer and 'at' is not the
proper manufacturer id according to the vendor-prefixes.

This patch takes the proper vendor-prefix and uses it for the eeprom
node.

Signed-off-by: Olliver Schinagl <oliver@schinagl.nl>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>