multimedia/avidemux: Fix build after b57d881bb6e9

Similar to f98927e2db26, mark NVDEC option BROKEN.

I'm fighting all of my urges to not relegate this to the pile since
there is still upstream activity [1] with promises of newer FFMpeg
and Qt6 support, but with no release since 2022, this is a *really*
slow burn.

[1] https://github.com/mean00/avidemux2

Reported by: pkg-fallout
MFH: 2026Q1