kfence: Defer the assignment of the local variable addr

The LoongArch architecture is different from other architectures. It
needs to update __kfence_pool during arch_kfence_init_pool().

This patch modifies the assignment location of the local variable addr
in the kfence_init_pool() function to support the case of updating
__kfence_pool in arch_kfence_init_pool().
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Enze Li <lienze@kylinos.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

mm/kfence/core.c

@@ -566,13 +566,14 @@ static void rcu_guarded_free(struct rcu_head *h)
  */
 static unsigned long kfence_init_pool(void)
 {
-	unsigned long addr = (unsigned long)__kfence_pool;
+	unsigned long addr;
 	struct page *pages;
 	int i;
 
 	if (!arch_kfence_init_pool())
-		return addr;
+		return (unsigned long)__kfence_pool;
 
+	addr = (unsigned long)__kfence_pool;
 	pages = virt_to_page(__kfence_pool);
 
 	/*