tests: i2c: i2c_target_api: fix test before size build assert addition

Fix the tests before a build time check is added to validate the
addressable size. Most tests have an eeprom size of 1024 defined but width
8-bit addressing, the majority of the eeprom cannot be addressed

Signed-off-by: Bram Vlerick <bram.vlerick@openpixelsystems.org>