mm: call __wb_calc_thresh instead of wb_calc_thresh in wb_over_bg_thresh

mm: call __wb_calc_thresh instead of wb_calc_thresh in wb_over_bg_thresh

Call __wb_calc_thresh to calculate wb bg_thresh of gdtc in
wb_over_bg_thresh to remove unnecessary wrap in wb_calc_thresh.

Link: https://lkml.kernel.org/r/20240425131724.36778-4-shikemeng@huaweicloud.com
Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Howard Cochran <hcochran@kernelspring.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>