Staging: hv: add driver_data to hv_vmbus_device_id

This is going to be needed by some drivers that handle more than one
device, like all other bus types do, so prepare for that in advance
before the user/kernel api is used.

Cc:  K. Y. Srinivasan <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>