drm/i915: Change WARN to ERROR in CSB count

There is no point in emitting a WARN since the backtrace will always be the
same. Errors have actually become easier to spot given the large number of WARNs
which exist today in modesetting paths.
Signed-off-by: NBen Widawsky <benjamin.widawsky@intel.com>
Reviewed-by: NMichel Thierry <michel.thierry@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452018609-10142-3-git-send-email-benjamin.widawsky@intel.comSigned-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_lrc.c

@@ -556,7 +556,9 @@ void intel_lrc_irq_handler(struct intel_engine_cs *ring)
 
 	spin_unlock(&ring->execlist_lock);
 
-	WARN(submit_contexts > 2, "More than two context complete events?\n");
+	if (unlikely(submit_contexts > 2))
+		DRM_ERROR("More than two context complete events?\n");
+
 	ring->next_context_status_buffer = write_pointer % GEN8_CSB_ENTRIES;
 
 	/* Update the read pointer to the old write pointer. Manual ringbuffer