ieee1394_core: switch to kthread API

This gets also rid of the MODPOST warning "drivers/ieee1394/ieee1394.o -
Section mismatch: reference to .exit.text: from .smp_locks after '' (at
offset 0x18)".

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jody McIntyre <scjody@modernduck.com>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Ben Collins <bcollins@ubuntu.com>