cpu/stm32/periph/dac: optimize setting DAC

[Enoch247]

Contribution description

The current implmentation right shifted the 16 bit value passed into dac_set() down to the 12 bits that the DAC is actually capable of. This patch drops the shift and instead writes the 16 bit value to the DAC's left aligned 12 bit wide data holding register.

Testing procedure

do something like:

#include "perip/dac.h"

int main(void)
{
    dac_set(DAC_LINE(0), 0xffff/2);
    return 0;
}

• observe DAC's output is half of vref

Issues/PRs references

• none known

[riot-ci]

Murdock results

✔️ PASSED

1134424 cpu/stm32/periph/dac: optimize setting DAC

Success	Failures	Total	Runtime
6931	0	6931	09m:52s

Artifacts

• Documentation preview

[benpicco]

bors merge

[bors]

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• Murdock
• static-tests
• tools-build-success