mm/mm_init.c: only align start of ZONE_MOVABLE on nodes with memory

At the beginning of find_zone_movable_pfns_for_nodes(), it has properly
set node_states[N_MEMORY] in early_calculate_totalpages().

Instead of iterating over all possible nodes, we can just do the alignment
on nodes with memory.

Link: https://lkml.kernel.org/r/20250211082900.10877-1-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Dev Jain <dev.jain@arm.com>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>