at24: Init dynamic bin_attribute structures

Commit 6992f533

 introduced this requirement.

Reported-by: Albrecht Dress <albrecht.dress@arcor.de>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>