MFC r298280

aacraid(4): Sanely copyin userland pointers and ensure that we don't get
anything janky from a user. (cturt)

aac(4) landergriffith+freebsdbugzilla@gmail.com pointed out that aac(4)
had the same issue and handling of pointers, so let's change that too.

PR: 206573
Submitted by: cturt@hardenedbsd.org