[PATCH] sg.c: fix a memory leak in devices seq_file implementation (2nd)

I know that scsi procfs is legacy code but this is a fix for a memory leak.

While reading through sg.c I realized that the implementation of
/proc/scsi/sg/devices with seq_file is leaking memory due to freeing the
pointer returned by the next() iterator method. Since next() might
return NULL or an error this is wrong. This patch fixes it through using
the seq_files private field for holding the reference to the iterator
object.

Here is a small bash script to trigger the leak. Use slabtop to watch
the size-32 usage grow and grow.

#!/bin/sh

while true; do
	cat /proc/scsi/sg/devices > /dev/null
done

Signed-off-by: Jan Blunck <j.blunck@tu-harburg.de>
Signed-off-by: Chris Wright <chrisw@osdl.org>