[PATCH] ipmi: missing NULL test for kthread

On IPMI systems with BT interfaces, we don't start the kernel thread, so
smi_info->thread is NULL.  Test for NULL when stopping the thread, because
kthread_stop() doesn't, and an oops ensues otherwise.

Signed-off-by: Matt Domsch <Matt_Domsch@dell.com>
Acked-by: Corey Minyard <minyard@acm.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>