drm/amd/pm: fix uninitialized variable warnings for vega10_hwmgr

[ Upstream commit 5fa7d540 ]

Clear warnings that using uninitialized variable when fails
to get the valid value from SMU.

Signed-off-by: Tim Huang <Tim.Huang@amd.com>
Reviewed-by: Yang Wang <kevinyang.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>