[Nouveau] pwr/macros: Stop playing Russian roulette on data memory

[Roy Spliet]

This patch fixes the pwr firmware to play nicely at least on NVA3. Because Martin might send more patches soon, I didn't include a regenerated nvXX.fuc.h. To me it makes more sense if all patches are merged then, and a final patch regenerates the headers in one go. Of course, I did test this patch and found it to work as intended, so feel free to pick up as you please.