Update build-ffmpeg

Author: markus-perl

build-ffmpeg

@@ -873,7 +873,7 @@ if [[ "$OSTYPE" == "linux-gnu" ]]; then
     if build "nv-codec" "11.1.5.2"; then
       download "https://github.com/FFmpeg/nv-codec-headers/releases/download/n11.1.5.2/nv-codec-headers-11.1.5.2.tar.gz"
       execute make PREFIX="${WORKSPACE}"
-      execute make install PREFIX="${WORKSPACE}"
+      execute make PREFIX="${WORKSPACE}/usr" install
       build_done "nv-codec" "11.1.5.2"
     fi
     CFLAGS+=" -I/usr/local/cuda/include"