Also fix one instance where access was done wrongly.
This makes certain that the split between MediaChannel types is respected
for this variable (prior to splitting the actual C++ types).
Bug: webrtc:13931
Change-Id: I8cf48ff5eddef35fda75533bb9c5075083c4ab16
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/305220
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40065}