Staging: hv: Fix up memory leak on HvCleanup

Don't assign NULL too early

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>