usbvision fix overflow of interfaces array

commit 588afcc1 upstream.

This fixes the crash reported in:
http://seclists.org/bugtraq/2015/Oct/35


The interface number needs a sanity check.

Signed-off-by: Oliver Neukum <oneukum@suse.com>
Cc: Vladis Dronov <vdronov@redhat.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
[bwh: Backported to 2.6.32: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Willy Tarreau <w@1wt.eu>