Staging: hv: remove TRUE, FALSE, and NULL usage

Don't define things that are either already provided (like NULL), or you
shouldn't use (like TRUE and FALSE).

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