drm/amdgpu: fix wrong sizeof argument

voltage_parameters is a point to a struct of type
SET_VOLTAGE_PARAMETERS_V1_3. Passing just voltage_parameters would
not print the right size of the struct variable. So we need to pass
*voltage_parameters to sizeof().

Fixes: 4630d503

 ("drm/amdgpu: check PS, WS index")
Signed-off-by: Samasth Norway Ananda <samasth.norway.ananda@oracle.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>