staging: erofs: complete error handing of z_erofs_map_blocks_iter

This patch completes error handing of z_erofs_map_blocks_iter
and vle_get_logical_extent_head, including no memory and
io error cases.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>