drm/i915: silence vblank warnings

these errors are pretty pointless

Reviewed-by: Jesse Barnes <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/i915/i915_irq.c

···
 	low_frame = pipe ? PIPEBFRAMEPIXEL : PIPEAFRAMEPIXEL;
 
 	if (!i915_pipe_enabled(dev, pipe)) {
-		DRM_ERROR("trying to get vblank count for disabled pipe %d\n", pipe);
+		DRM_DEBUG("trying to get vblank count for disabled pipe %d\n", pipe);
 		return 0;
 	}
 
···
 	int reg = pipe ? PIPEB_FRMCOUNT_GM45 : PIPEA_FRMCOUNT_GM45;
 
 	if (!i915_pipe_enabled(dev, pipe)) {
-		DRM_ERROR("trying to get vblank count for disabled pipe %d\n", pipe);
+		DRM_DEBUG("trying to get vblank count for disabled pipe %d\n", pipe);
 		return 0;
 	}