drm/i915: Use macro in place of open-coded for_each_universal_plane loop

This was the only use of (misleadingly-named) intel_num_planes()
function, so we can remove it as well.

Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1477522291-10874-3-git-send-email-matthew.d.roper@intel.com
Reviewed-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index 58d3ba0..6f19e60 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -4232,7 +4232,7 @@ static void skl_update_wm(struct drm_crtc *crtc)
 	if (crtc->state->active_changed) {
 		int plane;
 
-		for (plane = 0; plane < intel_num_planes(intel_crtc); plane++)
+		for_each_universal_plane(dev_priv, pipe, plane)
 			skl_write_plane_wm(intel_crtc, &pipe_wm->planes[plane],
 					   &results->ddb, plane);