commit 0b1d250a upstream.

Fix a NULL-pointer dereference in the interrupt callback should a
malicious device send data containing a bad port number by adding the
missing sanity check.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Johan Hovold <johan@kernel.org>
[bwh: Backported to 3.2:
 - Use &urb->dev->dev instead of local dev variable
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>