drm/amdgpu/soc15: fix xclk for raven

It's 25 Mhz (refclk / 4).  This fixes the interpretation
of the rlc clock counter.
Acked-by: NEvan Quan <evan.quan@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/soc15.c

@@ -272,7 +272,12 @@ static u32 soc15_get_config_memsize(struct amdgpu_device *adev)
 
 static u32 soc15_get_xclk(struct amdgpu_device *adev)
 {
-	return adev->clock.spll.reference_freq;
+	u32 reference_clock = adev->clock.spll.reference_freq;
+
+	if (adev->asic_type == CHIP_RAVEN)
+		return reference_clock / 4;
+
+	return reference_clock;
 }