USB: serial: whiteheat: fix potential slab corruption

Fix a user-controlled slab buffer overflow due to a missing sanity check
on the bulk-out transfer buffer used for control requests.

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/20191029102354.2733-2-johan@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>