staging: brcm80211: remove kernel_thread() for dhd_dpc_thread.

use kthread_run(), kthread_stop(), and kthread_should_stop().  Removes
dpc_pid, dpc_exited, and the call to DAEMONIZE.

dpc_tsk is NULL when not running.

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