USB: add URB_FREE_BUFFER to permissible flags

URB_FREE_BUFFER needs to be allowed in the sanity checks to use drivers that
use that flag.


Signed-off-by: Oliver Neukum <oneukum@suse.de>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>