drm/amd/swsmu: modify the gfx activity scaling

Add an if condition for gfx activity because the scaling has been changed after smu fw version 5d4600.
And remove a warning log.

Signed-off-by: Li Ma <li.ma@amd.com>
Reviewed-by: Yifan Zhang <yifan1.zhang@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org # 6.7.x