hwmon: (powerz) Avoid cacheline sharing for DMA buffer

In the Linux kernel, the following vulnerability has been resolved:

hwmon: (powerz) Avoid cacheline sharing for DMA buffer

Depending on the architecture the transfer buffer may share a cacheline

with the following mutex. As the buffer may be used for DMA, that is

problematic.

Use the high-level DMA helpers to make sure that cacheline sharing can

not happen.

Also drop the comment, as the helpers are documentation enough.

https://sashiko.dev/#/message/20260408175814.934BFC19421%40smtp.kernel.org