gma ddi: Don't try to disable non-existent DDI D

Didn't hurt on Haswell-/Broadwell-U, but did lock up Broxton.

Change-Id: I6a47d0fba8cb6e59d8ace1ab64eed6182769a37b
Signed-off-by: Nico Huber <nico.huber@secunet.com>
Reviewed-on: https://review.coreboot.org/18420
Tested-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
diff --git a/common/haswell_shared/hw-gfx-gma-connectors.adb b/common/haswell_shared/hw-gfx-gma-connectors.adb
index 15b3c12..734b11a 100644
--- a/common/haswell_shared/hw-gfx-gma-connectors.adb
+++ b/common/haswell_shared/hw-gfx-gma-connectors.adb
@@ -83,7 +83,7 @@
    procedure Post_All_Off
    is
    begin
-      for Port in Digital_Port range DIGI_A .. DIGI_D loop
+      for Port in Digital_Port range DIGI_A .. Config.Last_Digital_Port loop
          DDI.Off (Port);
       end loop;
       if Config.Is_FDI_Port (Analog) then