buildroot

gst1-libav: bump to version 1.8.3

Now that we moved to ffmpeg 3.x the build and runtime (when patched) problems
have gone away.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>