fix typo from commit 63349df2610a (fixes bug 5396)

configure

@@ -23033,7 +23033,7 @@ $as_echo "#define HAVE_INOTIFY 1" >>confdefs.h
                 ;;
         esac
     fi
-    LIBS="save_$LIBS"
+    LIBS="$save_LIBS"
 }
 
 CheckIBus()

configure.ac

@@ -2741,7 +2741,7 @@ CheckInotify()
                 ;;
         esac
     fi
-    LIBS="save_$LIBS"
+    LIBS="$save_LIBS"
 }
 
 dnl See if the platform has libibus IME support.