ARM: at91: Fix USBA gadget registration

Since 193ab2a6070039e7ee2b9b9bebea754a7c52fd1b, various AT91 boards don't
register USBA adapters anymore due to depending on a now non-existing
symbol. Fix the symbol name.

Signed-off-by: Jochen Friedrich <jochen@scram.de>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
CC: stable@kernel.org
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>