net: e1000: Fix the build with driver model and SPI EEPROM

When adding support for the driver model the SPI EEPROM feature had
been ignored. Fix the build with both CONFIG_DM_ETH and
CONFIG_E1000_SPI enabled.

Signed-off-by: Alban Bedel <alban.bedel@avionic-design.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>