Fix an OOB Write bug in avrc_vendor_msg

Plus some cleanup

Bug: 271962784
Test: manual
Ignore-AOSP-First: security
Tag: #security
(cherry picked from commit d5de235b)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:469492bcbdbd970f442f1978a1c63f454283d1de)
Merged-In: Ice5ad780ac0b177c73d84ed37960b4540df1ec86
Change-Id: Ice5ad780ac0b177c73d84ed37960b4540df1ec86