drm/i915: Fix assert_plane warning during FDI link train

assert_plane_enabled() is now triggering during FDI link train because
we no longer enable planes that early.

This problem got introduced in:
 commit a5c4d7bc
 Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
 Date:   Fri Mar 7 18:32:13 2014 +0200

    drm/i915: Disable/enable planes as the first/last thing during modeset on ILK+

Just drop the assert since we shouldn't need planes for link training.
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Squash in fixup for now unused plane local variable, reported
by 0-day tester.]
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -2599,12 +2599,10 @@ static void ironlake_fdi_link_train(struct drm_crtc *crtc)
 	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
 	int pipe = intel_crtc->pipe;
-	int plane = intel_crtc->plane;
 	u32 reg, temp, tries;
 
-	/* FDI needs bits from pipe & plane first */
+	/* FDI needs bits from pipe first */
 	assert_pipe_enabled(dev_priv, pipe);
-	assert_plane_enabled(dev_priv, plane);
 
 	/* Train 1: umask FDI RX Interrupt symbol_lock and bit_lock bit
 	   for train result */