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>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>