driver-core: make __device_attach() static

It is only used within dd.c and thus need not be global.
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/base/dd.c

@@ -517,7 +517,7 @@ static void __device_attach_async_helper(void *_dev, async_cookie_t cookie)
 	put_device(dev);
 }
 
-int __device_attach(struct device *dev, bool allow_async)
+static int __device_attach(struct device *dev, bool allow_async)
 {
 	int ret = 0;