gma pch-transcoder: Work around GNAT issue

The combination of the Shift_Left intrinsic and the case expression
somehow makes GNAT crash.

(cherry picked from commit 0dadb674cc98974378ccceccc8c557197a2bad16)

Original-Change-Id: Ibdb3ce4c1699d547999efd89ee6f4ae0f570703c
Original-Signed-off-by: Nico Huber <nico.huber@secunet.com>
Original-Reviewed-on: https://review.coreboot.org/c/libgfxinit/+/73163
Original-Reviewed-by: Elyes Haouas <ehaouas@noos.fr>
Original-Reviewed-by: Felix Singer <felixsinger@posteo.net>
Original-Tested-by: Nico Huber <nico.h@gmx.de>
GitOrigin-RevId: 0dadb674cc98974378ccceccc8c557197a2bad16
Change-Id: Ica22a67595aa9141eeaf817b20f19dc6abe13d10
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/coreboot/libgfxinit/+/4292346
Reviewed-by: Reka Norman <rekanorman@chromium.org>
Tested-by: CopyBot Service Account <copybot.service@gmail.com>
Commit-Queue: Reka Norman <rekanorman@chromium.org>

common/hw-gfx-gma-pch-transcoder.adb

diff --git a/common/hw-gfx-gma-pch-transcoder.adb b/common/hw-gfx-gma-pch-transcoder.adb
index eb1715f..04d15bb 100644
--- a/common/hw-gfx-gma-pch-transcoder.adb
+++ b/common/hw-gfx-gma-pch-transcoder.adb
@@ -37,11 +37,11 @@
       return Word32
    is
    begin
-      return Shift_Left (PLL,
-        (case Port is
-            when FDI_A => 0,
-            when FDI_B => 4,
-            when FDI_C => 8));
+      case Port is
+         when FDI_A => return Shift_Left (PLL, 0);
+         when FDI_B => return Shift_Left (PLL, 4);
+         when FDI_C => return Shift_Left (PLL, 8);
+      end case;
    end DPLL_SEL_TRANSCODER_x_DPLL_SEL;
 
    TRANS_CONF_TRANSCODER_ENABLE        : constant := 1 * 2 ** 31;