drm/i915: Silence _DSM errors

<@ajax> mjg59: how concerned should i be about [drm:intel_dsm_pci_probe]
        *ERROR* failed to get supported _DSM functions ?
<@mjg59> ajax: Entirely unconcerned

Signed-off-by: Adam Jackson <ajax@redhat.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_acpi.c b/drivers/gpu/drm/i915/intel_acpi.c
index cb91210..bae3edf 100644
--- a/drivers/gpu/drm/i915/intel_acpi.c
+++ b/drivers/gpu/drm/i915/intel_acpi.c
@@ -208,7 +208,7 @@
 
 	ret = intel_dsm(dhandle, INTEL_DSM_FN_SUPPORTED_FUNCTIONS, 0);
 	if (ret < 0) {
-		DRM_ERROR("failed to get supported _DSM functions\n");
+		DRM_DEBUG_KMS("failed to get supported _DSM functions\n");
 		return false;
 	}