rapidio: fix use after free in rio_unregister_scan()

We're freeing the list iterator so we can't move to the next entry.
Since there is only one matching mport_id, we can just break after
finding it.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Ryan Mallon <rmallon@gmail.com>
Acked-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>