USB: digi_acceleport: Fix broken unthrottle.

This patch fixes a regression introduced in
39892da4

.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Acked-by: Oliver Neukum <oliver@neukum.org>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>