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.comSigned-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>

mm/sparse.c

@@ -351,7 +351,7 @@ sparse_early_usemaps_alloc_pgdat_section(struct pglist_data *pgdat,
 again:
 	usage = memblock_alloc_try_nid(size, SMP_CACHE_BYTES, goal, limit, nid);
 	if (!usage && limit) {
-		limit = 0;
+		limit = MEMBLOCK_ALLOC_ACCESSIBLE;
 		goto again;
 	}
 	return usage;