Fix build due to merge of 75958420 and renaming due to 8eb87f0d

I.e. rename mVideoCallback -> mCallback. Line with original name
was added in mwd, renaming was done in master. The renaming CL
was cherry-picked to mwd (and build probably fixed there).

Change-Id: I462a0fedd00293a148404e1419740bf492ae5de9