drm/amd/powerplay: Delete a redundant memory setting in vega20_set_default_od8_setttings()

The memory was set to zero already by a call of the function “kzalloc”.
Thus remove an extra call of the function “memset” for this purpose.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>