patches: fixed grep

patches/patch.sh

@@ -259,7 +259,7 @@ case "$action" in
     fi
 
     echo ""
-    if grep -q $PLUMED_ROOT/src/config/compile_options.sh "-D__PLUMED_MPI=1"; then
+    if grep -q "D__PLUMED_MPI=1" $PLUMED_ROOT/src/config/compile_options.sh ; then
       echo "PLUMED is compiled with MPI support so you can configure $engine with MPI" 
     else
       echo "PLUMED is compiled WITHOUT MPI support so you CANNOT configure $engine with MPI"