[tests] Fix typo in Flags value.

TBR=jarin@chromium.org
NOTRY=true

Bug: v8:6447
Change-Id: Ied42c4ba8fc19f2441f6c2ffd31d3f56055ac487
Reviewed-on: https://chromium-review.googlesource.com/518823Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45616}

test/mjsunit/regress/regress-543994.js

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flass: --allow-natives-syntax --always-opt --gc-interval=163 --stress-compaction
+// Flags: --allow-natives-syntax --always-opt --gc-interval=163 --stress-compaction
 
 try { a = f();
 } catch(e) {