Upgrade libopus to 794392ecd77e6fc6aafa62c3f6002780abcc2c7c am: e135dd4b8a

Original change: https://android-review.googlesource.com/c/platform/external/libopus/+/1540686

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I1956c3ed41216e9dd8870fb2a82d2c2bb16e6b06