md/raid5-cache: do not need to set STRIPE_PREREAD_ACTIVE repeatedly

R5c_make_stripe_write_out has set this flag, do not need to set again.
Signed-off-by: NJackieLiu <liuyun01@kylinos.cn>
Signed-off-by: NShaohua Li <shli@fb.com>

drivers/md/raid5-cache.c

@@ -1247,8 +1247,6 @@ static void r5c_flush_stripe(struct r5conf *conf, struct stripe_head *sh)
 	atomic_inc(&conf->active_stripes);
 	r5c_make_stripe_write_out(sh);
 
-	if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
-		atomic_inc(&conf->preread_active_stripes);
 	raid5_release_stripe(sh);
 }