USB: keyspan: fix bogus array index

commit a07088098a650267b2eda689538133a324b9523f upstream.

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.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>