graphics/opendx: Correction to b63245a5.

- Broken for arm64, not amd64.

Reported by:	Thierry Thomas <thierry@freebsd.org>

graphics/opendx/Makefile

@@ -15,7 +15,7 @@ LICENSE_NAME=	IBM PUBLIC LICENSE - Open Visualization Data Explorer VERSION 1.0
 LICENSE_FILE=	${WRKSRC}/LICENSE
 LICENSE_PERMS=	dist-mirror dist-sell pkg-mirror pkg-sell auto-accept
 
-NOT_FOR_ARCHS=	amd64
+NOT_FOR_ARCHS=	arm64
 NOT_FOR_ARCHS_REASON=	does not build
 
 LIB_DEPENDS=	libtiff.so:graphics/tiff		\