ricv64: Update "Zbb" extension opcode comment. am: 81410830d5 am: a4305958cc

Original change: https://android-review.googlesource.com/c/platform/art/+/2967245

Change-Id: Ia9fe3a27a5393243dc08fbea358c443ffdb2a2a3
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>