blk-wbt: fix that 'rwb->wc' is always set to 1 in wbt_init()

stable inclusion
from stable-v5.10.152
commit 31b1570677e8bf85f48be8eb95e21804399b8295
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I60HVY
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=31b1570677e8bf85f48be8eb95e21804399b8295



-------------------------------

commit 285febab upstream.

commit 8c5035df ("blk-wbt: call rq_qos_add() after wb_normal is
initialized") moves wbt_set_write_cache() before rq_qos_add(), which
is wrong because wbt_rq_qos() is still NULL.

Fix the problem by removing wbt_set_write_cache() and setting 'rwb->wc'
directly. Noted that this patch also remove the redundant setting of
'rab->wc'.

Fixes: 8c5035df ("blk-wbt: call rq_qos_add() after wb_normal is initialized")
Reported-by: kernel test robot <yujie.liu@intel.com>
Link: https://lore.kernel.org/r/202210081045.77ddf59b-yujie.liu@intel.com


Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20221009101038.1692875-1-yukuai1@huaweicloud.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>