Seeing the watermark latency values in dmesg might help sometimes.

v2: Use DRM_ERROR() when expected latency values are missing

Note: We might hit the DRM_ERROR added in this patch and apparently
there's not much we can do about that. But I think it'd be interesting
to figure out whether that actually happens in the real world, so I
didn't apply a s/DRM_ERROR/DRM_DEBUG_KMS/ bikeshed while applying.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: NPaulo Zanoni <paulo.r.zanoni@intel.com>
[danvet: Add note about new error dmesg output.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>