drm/i915/vlv: Fix typo in the DPIO register define.

Incorrect definition DPIO_TX3_SWING_CTL4.

From Ville's review: "Based on the specs, the typo meant that HDMI B
ended up using "incorrect" de-emphasis for the TMDS data lanes."
Signed-off-by: Chon Ming Lee <chon.ming.lee@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Add comment from Ville's review about the impact.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -444,7 +444,7 @@
 
 #define _DPIO_TX3_SWING_CTL4_A		0x690
 #define _DPIO_TX3_SWING_CTL4_B		0x2a90
-#define DPIO_TX3_SWING_CTL4(pipe) _PIPE(pipe, _DPIO_TX_SWING_CTL4_A, \
+#define DPIO_TX3_SWING_CTL4(pipe) _PIPE(pipe, _DPIO_TX3_SWING_CTL4_A, \
 					_DPIO_TX3_SWING_CTL4_B)
 
 /*