drm/amdgpu/powerplay: Clean up errors in vega20_hwmgr.c

Fix the following errors reported by checkpatch:

ERROR: code indent should use tabs where possible
ERROR: space required before the open parenthesis '('
ERROR: space prohibited before that close parenthesis ')'

Signed-off-by: Ran Sun <sunran001@208suo.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>