drm/amd/pm: drop unnecessary manual mode check

As the fan control was guarded under manual mode before fan speed
RPM/PWM setting. Thus the extra check is totally redundant.

Signed-off-by: Evan Quan <evan.quan@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>