Staging: hv: make the Hyper-V virtual bus code build

The #define KERNEL_2_6_27 needs to be set, and I adjusted the include
directories a bit to get things to build properly.

I also fixed up the direct access of bus_id, as that field is now gone.

The hv_vmbus code should now build properly, with no errors.

Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>