fixes building and installing against tree specified in

Fixed installing kdbus against spocified modules directory (install, uninstalled was using (uname -r)).

<code>
KERNELDIR=/lib/modules/3.16.0-rc1-next-20140618-git+/build make install
</code>
now correctly installs modules into /lib/modules/3.16.0-rc1-next-20140618-git+/kernel/drivers/kdbus/.