rcu: Remove useless "ret" update in rcu_gp_fqs_loop()

Within rcu_gp_fqs_loop(), the "ret" local variable is set to the
return value from swait_event_idle_timeout_exclusive(), but "ret" is
unconditionally overwritten later in the code.  This commit therefore
removes this useless assignment.
Signed-off-by: Liu Song <liu.song11@zte.com.cn>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tree.c

@@ -1954,8 +1954,8 @@ static noinline_for_stack void rcu_gp_fqs_loop(void)
 		trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq,
 				       TPS("fqswait"));
 		WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS);
-		ret = swait_event_idle_timeout_exclusive(
-				rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j);
+		(void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq,
+				 rcu_gp_fqs_check_wake(&gf), j);
 		rcu_gp_torture_wait();
 		WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS);
 		/* Locking provides needed memory barriers. */