[PATCH] Stop adjusting info->max_mapnr when no mem_maps are found.

If mem_maps are allocated with remap allocator, makedumpfile can't
find them without vmlinux. In that case, info->max_mapnr will be
truncated to 0 and there will be no page data in a dump file.

This patch enables the environment above to make full dump at
least.

Signed-off-by: Atsushi Kumagai <kumagai-atsushi@mxc.nes.nec.co.jp>