ext4: flag as supporting buffered async reads

ext4 uses generic_file_read_iter(), which already supports this.

Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Link: https://lore.kernel.org/r/fb90cc2d-b12c-738f-21a4-dd7a8ae0556a@kernel.dk


Signed-off-by: Theodore Ts'o <tytso@mit.edu>