drm/amdgpu/soc21: fix xclk for APUs

The reference clock is supposed to be 100Mhz, but it
appears to actually be slightly lower (99.81Mhz).

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/14451
Reviewed-by: Jesse Zhang <Jesse.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Author: alexdeucher

drivers/gpu/drm/amd/amdgpu/soc21.c

@@ -256,7 +256,13 @@ static u32 soc21_get_config_memsize(struct amdgpu_device *adev)
 
 static u32 soc21_get_xclk(struct amdgpu_device *adev)
 {
-	return adev->clock.spll.reference_freq;
+	u32 reference_clock = adev->clock.spll.reference_freq;
+
+	/* reference clock is actually 99.81 Mhz rather than 100 Mhz */
+	if ((adev->flags & AMD_IS_APU) && reference_clock == 10000)
+		return 9981;
+
+	return reference_clock;
 }