staging: brcm80211: remove kernel_thread() for dhd_watchdog_thread.

Replaced kernel_thread() with kthread_run().  Used kthread_should_stop()
in place of watchdog_exited completion.  Replaced watchdog_pid with
struct task_struct.

watchdog_tsk is NULL when the task is not running.

Signed-off-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>