btrfs: remove dead assignment in prepare_one_folio()

btrfs: remove dead assignment in prepare_one_folio()

In prepare_one_folio(), ret is initialized to 0 at declaration,
and in an error path we assign ret = 0 before jumping to the
again label to retry the operation. However, ret is immediately
overwritten by ret = set_folio_extent_mapped(folio) after the
again label.

Both assignments are never observed by any code path,
therefore they can be safely removed.

Signed-off-by: Massimiliano Pellizzer <mpellizzer.dev@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>