tipc: improve function tipc_wait_for_cond()

Commit 844cf763 ("tipc: make macro tipc_wait_for_cond() smp safe")
replaced finish_wait() with remove_wait_queue() but still used
prepare_to_wait(). This causes unnecessary conditional
checking  before adding to wait queue in prepare_to_wait().

This commit replaces prepare_to_wait() with add_wait_queue()
as the pair function with remove_wait_queue().
Acked-by: NYing Xue <ying.xue@windriver.com>
Acked-by: NJon Maloy <jon.maloy@ericsson.com>
Signed-off-by: NTung Nguyen <tung.q.nguyen@dektech.com.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/tipc/socket.c

@@ -388,7 +388,7 @@ static int tipc_sk_sock_err(struct socket *sock, long *timeout)
 		rc_ = tipc_sk_sock_err((sock_), timeo_);		       \
 		if (rc_)						       \
 			break;						       \
-		prepare_to_wait(sk_sleep(sk_), &wait_, TASK_INTERRUPTIBLE);    \
+		add_wait_queue(sk_sleep(sk_), &wait_);                         \
 		release_sock(sk_);					       \
 		*(timeo_) = wait_woken(&wait_, TASK_INTERRUPTIBLE, *(timeo_)); \
 		sched_annotate_sleep();				               \