drm/i915: Avoid spurious WARNs about the wrong pipe in the PPS code

Until recently vlv_steal_power_sequencer() wasn't being called for
normal DP ports, and hence it could assert that it should only be
called for pipe A and B (since pipe C doesn't support eDP). However
that changed when we started to consider normal DP ports as well when
choosing a PPS. So we will now get spurious warnings when
vlv_steal_power_sequencer() does get called for pipe C. Avoid this by
moving the WARN down into vlv_detach_power_sequencer() where this
assertion should still hold.

Cc: Imre Deak <imre.deak@intel.com>
Cc: stable@vger.kernel.org
Fixes: 9f2bdb006a7e ("drm/i915: Prevent PPS stealing from a normal DP port on VLV/CHV")
References: https://bugs.freedesktop.org/show_bug.cgi?id=95287
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170208175254.10958-1-ville.syrjala@linux.intel.com
Reviewed-by: Imre Deak <imre.deak@intel.com>
(cherry picked from commit d158694f452252d0fef335a775aeb3eb74fe7af0)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dp.c

@@ -2887,6 +2887,9 @@ static void vlv_detach_power_sequencer(struct intel_dp *intel_dp)
 
 	WARN_ON(intel_dp->active_pipe != INVALID_PIPE);
 
+	if (WARN_ON(pipe != PIPE_A && pipe != PIPE_B))
+		return;
+
 	edp_panel_vdd_off_sync(intel_dp);
 
 	/*
@@ -2914,9 +2917,6 @@ static void vlv_steal_power_sequencer(struct drm_device *dev,
 
 	lockdep_assert_held(&dev_priv->pps_mutex);
 
-	if (WARN_ON(pipe != PIPE_A && pipe != PIPE_B))
-		return;
-
 	for_each_intel_encoder(dev, encoder) {
 		struct intel_dp *intel_dp;
 		enum port port;