mm/cma_debug: fix debugging alloc/free interface

CMA has alloc/free interface for debugging.  It is intended that
alloc/free occurs in specific CMA region, but, currently, alloc/free
interface is on root dir due to the bug so we can't select CMA region
where alloc/free happens.

This patch fixes this problem by making alloc/free interface per CMA
region.

Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: Michal Nazarewicz <mina86@mina86.com>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: Stefan Strogin <stefan.strogin@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/cma_debug.c

@@ -170,10 +170,10 @@ static void cma_debugfs_add_one(struct cma *cma, int idx)
 
 	tmp = debugfs_create_dir(name, cma_debugfs_root);
 
-	debugfs_create_file("alloc", S_IWUSR, cma_debugfs_root, cma,
+	debugfs_create_file("alloc", S_IWUSR, tmp, cma,
 				&cma_alloc_fops);
 
-	debugfs_create_file("free", S_IWUSR, cma_debugfs_root, cma,
+	debugfs_create_file("free", S_IWUSR, tmp, cma,
 				&cma_free_fops);
 
 	debugfs_create_file("base_pfn", S_IRUGO, tmp,