Rename libav.regression.ref --> lavf.regression.ref.

This matches the new name of the test target.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@18229 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

diff --git a/tests/libav.regression.ref b/tests/lavf.regression.ref
similarity index 100%
rename from tests/libav.regression.ref
rename to tests/lavf.regression.ref