mm/sparse: use MEMBLOCK_ALLOC_ACCESSIBLE enum instead of 0

Setting 'limit' variable to 0 might seem like it means "no limit".  But in
the memblock API, 0 actually means the 'MEMBLOCK_ALLOC_ACCESSIBLE' enum,
which limits the physical address range end based on
'memblock.current_limit'.  This could be confusing.

Use the enum instead of 0 to make it clear.

Link: https://lkml.kernel.org/r/20240610151528.943680-1-lsahn@wewakecorp.com


Signed-off-by: Leesoo Ahn <lsahn@ooseel.net>
Acked-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>