version.sh: make it independant of version.h file name

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

version.sh

@@ -40,9 +40,9 @@ if [ -z "$2" ]; then
 fi
 
 NEW_REVISION="#define FFMPEG_VERSION \"$version\""
-OLD_REVISION=$(cat version.h 2> /dev/null)
+OLD_REVISION=$(cat "$2" 2> /dev/null)
 
-# Update version.h only on revision changes to avoid spurious rebuilds
+# Update version header only on revision changes to avoid spurious rebuilds
 if test "$NEW_REVISION" != "$OLD_REVISION"; then
     echo "$NEW_REVISION" > "$2"
 fi