USB: legousbtower: fix slab info leak at probe

Make sure to check for short transfers when retrieving the version
information at probe to avoid leaking uninitialised slab data when
logging it.

Fixes: 1da177e4

 ("Linux-2.6.12-rc2")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20190919083039.30898-2-johan@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>