selftests/vm/run_vmtests: Fix wrong comment

A comment in `run_vmtests` is wrong because it is saying `128MB + 128MB
== 258MB`.  This commit fixes the comment.
Signed-off-by: NSeongJae Park <sj38.park@gmail.com>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/vm/run_vmtests

@@ -106,7 +106,7 @@ fi
 echo "---------------------------"
 echo "running userfaultfd_hugetlb"
 echo "---------------------------"
-# 258MB total huge pages == 128MB src and 128MB dst
+# 256MB total huge pages == 128MB src and 128MB dst
 ./userfaultfd_hugetlb 128 32 $mnt/ufd_test_file
 if [ $? -ne 0 ]; then
 	echo "[FAIL]"