btrfs: use KMEM_CACHE() to create btrfs_free_space cache

Use the KMEM_CACHE() macro instead of kmem_cache_create() to simplify
the creation of SLAB caches when the default values are used.
Signed-off-by: Kunwu Chan <chentao@kylinos.cn>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/free-space-cache.c

@@ -4154,9 +4154,7 @@ int btrfs_set_free_space_cache_v1_active(struct btrfs_fs_info *fs_info, bool act
 
 int __init btrfs_free_space_init(void)
 {
-	btrfs_free_space_cachep = kmem_cache_create("btrfs_free_space",
-			sizeof(struct btrfs_free_space), 0,
-			SLAB_MEM_SPREAD, NULL);
+	btrfs_free_space_cachep = KMEM_CACHE(btrfs_free_space, SLAB_MEM_SPREAD);
 	if (!btrfs_free_space_cachep)
 		return -ENOMEM;