Fix error message description in Checker

Change-Id: Ieaecd430b096f91cc41af6354ee82176fe60a037
diff --git a/tools/checker/match/line.py b/tools/checker/match/line.py
index 711d814..ce11e2a 100644
--- a/tools/checker/match/line.py
+++ b/tools/checker/match/line.py
@@ -41,7 +41,7 @@
       if expression.name in variables:
         pattern = re.escape(variables[expression.name])
       else:
-        Logger.testFailed("Multiple definitions of variable \"{}\"".format(expression.name),
+        Logger.testFailed("Missing definition of variable \"{}\"".format(expression.name),
                           pos.fileName, pos.lineNo)
     else:
       pattern = expression.pattern