multimedia/vvenc: unbreak on armv7, powerpc, i386 - builds fine

armv7 needs -Wno-error:
/wrkdirs/usr/ports/multimedia/vvenc/work/vvenc-1.13.0/source/Lib/CommonLib/arm/neon/InterpolationFilter_neon.cpp:708:9: error: unused variable 'src8tOff' [-Werror,-Wunused-variable]

708 |     int src8tOff = cStride;
    |         ^~~~~~~~

1 error generated.