thp: remove wake_up_interruptible in the exit path

Add the check of kthread_should_stop() to the conditions which are used to
wakeup on khugepaged_wait, then kthread_stop is enough to let the thread
exit

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>