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

fs/ext4/file.c

@@ -844,7 +844,7 @@ static int ext4_file_open(struct inode *inode, struct file *filp)
 			return ret;
 	}
 
-	filp->f_mode |= FMODE_NOWAIT;
+	filp->f_mode |= FMODE_NOWAIT | FMODE_BUF_RASYNC;
 	return dquot_file_open(inode, filp);
 }