omxvideoenc: Remove unneeded size check
omxvideoenc: Remove unneeded size check

We only enter this branch if nFilledLen > 0, there is not need
to check again.

https://bugzilla.gnome.org/show_bug.cgi?id=715192

GStreamer/gst-omx,GStreamer/gst-omx,GStreamer/gst-omx