fix use-after-free in adbd_auth

The writev call is using references to data from the packet after it's
popped from the queue. This was discovered in GrapheneOS due to using
zero-on-free by default. It ends up resulting in adb being unable to
persistently whitelist keys.

Change-Id: Ibd9c1c4170bfe632b598b7666d09e4ce939a9e95