aufs: for linux-v5.14-rc1, replace kmalloc_index() by __kmalloc_index()

In mainline, by the commit
	588c7fa022d7b 2021-06-29 mm, slub: change run-time assertion
		in kmalloc_index() to compile-time
kmalloc_index() stopped supporting the non-constant parameter.
But aufs wants to keep passing the non-constant parameter.  So replace
them by __kmalloc_index() with adding 'false' parameter.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/module.h

@@ -84,7 +84,7 @@ static inline void au_kfree_small(const void *p)
 static inline int au_kmidx_sub(size_t sz, size_t new_sz)
 {
 #ifndef CONFIG_SLOB
-	return kmalloc_index(sz) - kmalloc_index(new_sz);
+	return __kmalloc_index(sz, false) - __kmalloc_index(new_sz, false);
 #else
 	return -1; /* SLOB is untested */
 #endif