Revert "mm/filemap: avoid buffered read/write race to read inconsistent data"

This reverts commit e2c27b80

 ("mm/filemap: avoid buffered read/write
race to read inconsistent data"). After making the i_size_read/write
helpers be smp_load_acquire/store_release(), it is already guaranteed that
changes to page contents are visible before we see increased inode size,
so the extra smp_rmb() in filemap_read() can be removed.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240124142857.4146716-3-libaokun1@huawei.com
Signed-off-by: Christian Brauner <brauner@kernel.org>