USB: fix typo in drivers/usb/gadget/Kconfig

This tiny patch fixes a typo in drivers/usb/gadget/Kconfig. The typo
is present in 2.6.18-rc4 and in the corresponding -mm tree (and AFAIK,
FYI and FWIW was present in previous kernel versions as well).

From: Jules Villard <jvillard@ens-lyon.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>