driver-core: make __device_attach() static

It is only used within dd.c and thus need not be global.

Change-Id: I098406c6aa42f1360437224c727e8bdcecbcf3d1
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>
Git-commit: 802a87fd5be9cac1d05879bcdae2620e46b0dbe6
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>