m68k: mm: fix node memblock init

After pulling 5.7.0 (linux-next merge), mcf5441x mmu boot was
hanging silently.

memblock_add() seems not appropriate, since using MAX_NUMNODES
as node id, while memblock_add_node() sets up memory for node id 0.

Signed-off-by: Angelo Dureghello <angelo.dureghello@timesys.com>
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Greg Ungerer <gerg@linux-m68k.org>