USB: keyspan: fix bogus array index

The outcont_endpoints array was indexed using the port minor number
(which can be greater than the array size) rather than the device port
number.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>