loop: add file_start_write() and file_end_write()

loop: add file_start_write() and file_end_write()

file_start_write() and file_end_write() should be added around ->write_iter().

Recently we switch to ->write_iter() from vfs_iter_write(), and the
implied file_start_write() and file_end_write() are lost.

Also we never add them for dio code path, so add them back for covering
both.

Cc: Jeff Moyer <jmoyer@redhat.com>
Fixes: f2fed441c69b ("loop: stop using vfs_iter_{read,write} for buffered I/O")
Fixes: bc07c10a3603 ("block: loop: support DIO & AIO")
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250527153405.837216-1-ming.lei@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>