tools/memory-model: Fix checkalllitmus.sh comment

The checkalllitmus.sh runs litmus tests in the litmus-tests directory,
not those in the github archive, so this commit updates the comment to
reflect this reality.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/memory-model/scripts/checkalllitmus.sh

@@ -30,8 +30,8 @@ else
 	exit 255
 fi
 
-# Create any new directories that have appeared in the github litmus
-# repo since the last run.
+# Create any new directories that have appeared in the litmus-tests
+# directory since the last run.
 if test "$LKMM_DESTDIR" != "."
 then
 	find $litmusdir -type d -print |