drm/amd/pp: Convert voltage unit in mV*4 to mV on CZ/ST

the voltage showed in debugfs and hwmon should be in mV

Reviewed-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org