An attempt to use DMA on DAC on L476 panics

[mbq]

Hello, I'm attempting to writing something like waveform_generator.rs for L476; unfortunately an attempt to use write_dma() ends up in panic:

ERROR panicked at [...]/stm32-hal2-1.8.2/src/dma.rs:304:18:
not implemented

Apparently the channel selection for dac is just commented out there...

[David-OConnor]

I just pushed a commit that should fix this.

[mbq]

Thanks; now the panic is gone, however the DMA seem to do nothing (DAC output stays at 0), while direct writes with write_voltage() work as expected.