drm/i915: Fix incorrect comment

While the comment singles out Port A or B, the code says Port A or *D*.
Looking at the history it seems that the comment was added after the code,
so it seems likely that the code is correct, not the comment.

CC: Jani Nikula <jani.nikula@intel.com>
CC: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: David Weinehall <david.weinehall@linux.intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180209130755.11893-1-david.weinehall@linux.intel.com

drivers/gpu/drm/i915/intel_dp.c

@@ -256,7 +256,7 @@ static int cnl_max_source_rate(struct intel_dp *intel_dp)
 	if (IS_CNL_WITH_PORT_F(dev_priv))
 		return 810000;
 
-	/* For other SKUs, max rate on ports A and B is 5.4G */
+	/* For other SKUs, max rate on ports A and D is 5.4G */
 	if (port == PORT_A || port == PORT_D)
 		return 540000;