USB: usb/storage/initializers.c: fix signedness difference

fix warnings:
drivers/usb/storage/initializers.c:83:26: warning: incorrect type in argument 5 (different signedness)
drivers/usb/storage/initializers.c:83:26:    expected unsigned int *act_len
drivers/usb/storage/initializers.c:83:26:    got int *<noident>
drivers/usb/storage/initializers.c:89:26: warning: incorrect type in argument 5 (different signedness)
drivers/usb/storage/initializers.c:89:26:    expected unsigned int *act_len
drivers/usb/storage/initializers.c:89:26:    got int *<noident>

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>