ieee1394: Fix kthread stopping in nodemgr_host_thread

The nodemgr host thread can exit on its own even when kthread_should_stop
is not true, on receiving a signal (might never happen in practice, as
it ignores signals). But considering kthread_stop() must not be mixed with
kthreads that can exit on their own, I think changing the code like this
is clearer. This change means the thread can cut its sleep short when
receive a signal but looking at the code around, that sounds okay (and
again, it might never actually recieve a signal in practice).

Signed-off-by: Satyam Sharma <satyam@infradead.org>
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>