fs/buffer: remove bh_submit_read() helper

bh_submit_read() has no user anymore, just remove it.

Link: https://lkml.kernel.org/r/20220901133505.2510834-15-yi.zhang@huawei.com


Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>