bug fix: register the miopen_fusion op. (#1267)

One-line fix to register the op miopen_fusion. This error was causing loading of compiled model files (*.mxr) to fail.

src/targets/gpu/fuse_ops.cpp

@@ -677,6 +677,7 @@ struct miopen_fusion
         return args.back();
     }
 };
+MIGRAPHX_REGISTER_OP(miopen_fusion)
 
 struct miopen_conv_bias
 {