[dice] Update DICE_PRIVATE_KEY_SIZE to DICE_PRIVATE_KEY_BUFFER_SIZE

To adapt to the upstream open-dice change.

Bug: 357008987
Test: atest MicrodroidHostTests
Change-Id: I00f70d1216b6ff94020cadb3efcd74bf5f61807a
diff --git a/libs/dice/open_dice/Android.bp b/libs/dice/open_dice/Android.bp
index 4241c47..f799fb1 100644
--- a/libs/dice/open_dice/Android.bp
+++ b/libs/dice/open_dice/Android.bp
@@ -156,7 +156,7 @@
         "--allowlist-var=DICE_INLINE_CONFIG_SIZE",
         "--allowlist-var=DICE_PRIVATE_KEY_SEED_SIZE",
         "--allowlist-var=DICE_ID_SIZE",
-        "--allowlist-var=DICE_PRIVATE_KEY_SIZE",
+        "--allowlist-var=DICE_PRIVATE_KEY_BUFFER_SIZE",
     ],
 }