drm/i915: don't write TU size to N1 reg

TU size is only part of the M1 and M2 regs, not the N regs.  This keeps
us from overwriting a reserved field.

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -4170,7 +4170,7 @@ static int intel_crtc_mode_set(struct drm_crtc *crtc,
 
 	if (HAS_PCH_SPLIT(dev)) {
 		I915_WRITE(data_m1_reg, TU_SIZE(m_n.tu) | m_n.gmch_m);
-		I915_WRITE(data_n1_reg, TU_SIZE(m_n.tu) | m_n.gmch_n);
+		I915_WRITE(data_n1_reg, m_n.gmch_n);
 		I915_WRITE(link_m1_reg, m_n.link_m);
 		I915_WRITE(link_n1_reg, m_n.link_n);