[dice] Update DICE_PRIVATE_KEY_SIZE to DICE_PRIVATE_KEY_BUFFER_SIZE am: e9867a071a am: 0794526c37

Original change: https://android-review.googlesource.com/c/trusty/lib/+/3367823

Change-Id: I6b125a59c7e9cdf552bef72b2c33108708f9fb4d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>