i2c/eeprom: Hide Sony Vaio serial numbers

The sysfs interface to DMI data takes care to not make the system
serial number and UUID world-readable, presumably due to privacy
concerns. For consistency, we should not let the eeprom driver
export these same strings to the world on Sony Vaio laptops.
Instead, only make them readable by root, as we already do for BIOS
passwords.

Signed-off-by: Jean Delvare <khali@linux-fr.org>