ArmVirtPkg/PlatformBootManagerLib: eliminate unchecked PcdSetXX() calls

These are deprecated / disabled under the
DISABLE_NEW_DEPRECATED_INTERFACES feature test macro.

Introduce a variable called PcdStatus, and use it to assert the success of
these operations (there is no reason for them to fail here).

Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=165
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Tested-by: Ard Biesheuvel <ard.biesheuvel@linaro.org> # RVCT
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>

ArmVirtPkg/Library/PlatformBootManagerLib/PlatformBm.c

@@ -578,6 +578,8 @@ PlatformBootManagerBeforeConsole (
   VOID
   )
 {
+  RETURN_STATUS PcdStatus;
+
   //
   // Signal EndOfDxe PI Event
   //
@@ -629,7 +631,9 @@ PlatformBootManagerBeforeConsole (
   //
   // Set the front page timeout from the QEMU configuration.
   //
-  PcdSet16 (PcdPlatformBootTimeOut, GetFrontPageTimeoutFromQemu ());
+  PcdStatus = PcdSet16S (PcdPlatformBootTimeOut,
+                GetFrontPageTimeoutFromQemu ());
+  ASSERT_RETURN_ERROR (PcdStatus);
 
   //
   // Register platform-specific boot options and keyboard shortcuts.