drm/amd/pm: make the error log more clear for fine grain tuning function

This patch is to make the error log more clear for fine grain tuning
function, it covers Raven/Raven2/Picasso/Renoir/Vangogh.
The fine grain tuning function uses the sysfs file -- pp_od_clk_voltage,
but only when another sysfs file -- power_dpm_force_performance_level is
switched to "manual" mode, it is allowed to access "pp_od_clk_voltage".

Signed-off-by: Xiaojian Du <Xiaojian.Du@amd.com>
Acked-by: Huang Rui <ray.huang@amd.com>
Acked-by: Kevin Wang <kevin1.wang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>