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>
diff --git a/drivers/base/dd.c b/drivers/base/dd.c
index 3929253..42e97d90 100644
--- a/drivers/base/dd.c
+++ b/drivers/base/dd.c
@@ -517,7 +517,7 @@
 	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;