netfs: release readahead folios on iterator preparation failure

netfs: release readahead folios on iterator preparation failure

netfs_prepare_read_iterator() batches readahead folios in put_batch so that
the folio references can be dropped after the I/O iterator has been
prepared.

If rolling_buffer_load_from_ra() fails after earlier folios have been
batched, the function returns immediately and leaves those references held.
Release the batch before returning the error.

Fixes: 06fa229ceb36 ("netfs: Abstract out a rolling folio buffer implementation")
Signed-off-by: Yichong Chen <chenyichong@uniontech.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260727130716.1099906-4-dhowells@redhat.com
cc: Paulo Alcantara <pc@manguebit.org>
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>