drm/amd/powerplay: remove redundant memset

[Markus Elfring]

> kzalloc has already zeroed the memory.
> So the memset is unneeded.

See also a previous patch:
drm/amd/powerplay: Delete a redundant memory setting in vega20_set_default_od8_setttings()
https://lore.kernel.org/lkml/de3f6a5e-8ac4-bc8e-0d0c-3a4a5db283e9@web.de/
https://lore.kernel.org/patchwork/patch/1089691/
https://lkml.org/lkml/2019/6/17/460

Regards,
Markus