drm/vmwgfx: add Zack Rusin as maintainer

Reviewed-by: Zack Rusin <zackr@vmware.com>
Signed-off-by: Roland Scheidegger <sroland@vmware.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Link: https://patchwork.freedesktop.org/patch/414043/?series=85516&rev=2

MAINTAINERS

@@ -5784,6 +5784,7 @@ F:	drivers/gpu/drm/vboxvideo/
 DRM DRIVER FOR VMWARE VIRTUAL GPU
 M:	"VMware Graphics" <linux-graphics-maintainer@vmware.com>
 M:	Roland Scheidegger <sroland@vmware.com>
+M:	Zack Rusin <zackr@vmware.com>
 L:	dri-devel@lists.freedesktop.org
 S:	Supported
 T:	git git://people.freedesktop.org/~sroland/linux