DSP: latch dma parameters

This needs to be tested a fair bit before it could be considered a candidate for merging.
DSP wasn't latching DMA parameters appropriately and it could break the audio output.

I don't have an extensive title collection, but if people could test this PR (windows binary: https://dl.dolphin-emu.org/prs/pr-692-dolphin-latest-x64.7z) and report any regressions, that would be awesome.
I don't see why we'd change conventional indentation just for lambdas. Since it's essentially a 'function inside a function' (not exactly, but you get the point) it should be indented as if it were one.