package.sh: use only defined variables

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@53577 15284696-431f-4ddb-bdfa-cd5b030d7da7

mswindows/osgeo4w/package.sh

@@ -73,8 +73,8 @@ else
     GRASS_EXECUTABLE=grass${MAJOR}${MINOR}
 fi
 
-export GRASS_PYTHON="/c/OSGeo4W/bin/python.exe"
-export PYTHONHOME="/c/OSGeo4W/apps/Python27"
+export GRASS_PYTHON="$OSGEO4W_ROOT_MSYS/bin/python.exe"
+export PYTHONHOME="$OSGEO4W_ROOT_MSYS/apps/Python27"
 
 if [ -f mswindows/osgeo4w/package.log ]; then 
     i=0