workqueue: reuse the already calculated pwq in try_to_grab_pending()

try_to_grab_pending() was re-calculating the associated pwq using
get_work_pwq() when it already has it cached in a local varible and
the association can't change.  Reuse the local variable instead.

This doesn't introduce any functional changes.

tj: Updated description.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -1225,7 +1225,7 @@ static int try_to_grab_pending(struct work_struct *work, bool is_dwork,
 			pwq_activate_delayed_work(work);
 
 		list_del_init(&work->entry);
-		pwq_dec_nr_in_flight(get_work_pwq(work), get_work_color(work));
+		pwq_dec_nr_in_flight(pwq, get_work_color(work));
 
 		/* work->data points to pwq iff queued, point to pool */
 		set_work_pool_and_keep_pending(work, pool->id);