erofs: fix missing unmap if z_erofs_get_extent_compressedlen() fails

Otherwise, meta buffers could be leaked.

Fixes: cec6e93bea ("erofs: support parsing big pcluster compress indexes")
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20221205150050.47784-1-hsiangkao@linux.alibaba.com

fs/erofs/zmap.c

@@ -694,7 +694,7 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 		map->m_pa = blknr_to_addr(m.pblk);
 		err = z_erofs_get_extent_compressedlen(&m, initial_lcn);
 		if (err)
-			goto out;
+			goto unmap_out;
 	}
 
 	if (m.headtype == Z_EROFS_VLE_CLUSTER_TYPE_PLAIN) {
@@ -718,14 +718,12 @@ static int z_erofs_do_map_blocks(struct inode *inode,
 		if (!err)
 			map->m_flags |= EROFS_MAP_FULL_MAPPED;
 	}
+
 unmap_out:
 	erofs_unmap_metabuf(&m.map->buf);
-
-out:
 	erofs_dbg("%s, m_la %llu m_pa %llu m_llen %llu m_plen %llu m_flags 0%o",
 		  __func__, map->m_la, map->m_pa,
 		  map->m_llen, map->m_plen, map->m_flags);
-
 	return err;
 }