USB: digi_acceleport: do sanity checking for the number of ports

The driver can be crashed with devices that expose crafted descriptors
with too few endpoints.

See: http://seclists.org/bugtraq/2016/Mar/61



Change-Id: I6b91e4e48dd4ffb7ad959461e7dc33b2fd1f6a50
Signed-off-by: Oliver Neukum <ONeukum@suse.com>
[johan: fix OOB endpoint check and add error messages ]
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>