ffmpeg: fix version script to produce correct ffmpeg version

Currently it outputs the LibreELEC git version (eg. 7.95.1-1538-g077ed6e) and
not ffmpeg version (eg. 3.3.2-30554d7).

packages/multimedia/ffmpeg/patches/ffmpeg-00.0000-fix-version-script.patch

@@ -0,0 +1,14 @@
+diff --git a/version.sh b/version.sh
+index edc4dd3..d2b90a9 100755
+--- a/version.sh
++++ b/version.sh
+@@ -16,6 +16,9 @@ fi
+ test "$revision" || revision=$(cd "$1" &&
+   git log -1 --pretty=format:"git-%cd-%h" --date=short 2> /dev/null)
+ 
++# ignore any current revision, which is just that of the LibreELEC repository
++revision=
++
+ # Snapshots from gitweb are in a directory called ffmpeg-hhhhhhh or
+ # ffmpeg-HEAD-hhhhhhh.
+ if [ -z "$revision" ]; then