x86/platform/hyperv: Handle VMBUS driver being a module

Hyper-V VMBUS driver can be a module; handle this case
correctly. Please apply.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Cc: olaf@aepfle.de
Cc: apw@canonical.com
Cc: jasowang@redhat.com
Link: http://lkml.kernel.org/r/1396421502-23222-1-git-send-email-kys@microsoft.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>