selftests/ftrace: Fix required features for VFS type test case

Since the VFS type argument test case uses fprobe events, it must
check the availablity of dynamic_events file and fprobe events syntax
in README. Without this fix, the test fails if CONFIG_FPROBE_EVENTS=n.

Link: https://lore.kernel.org/all/171478301645.110267.464634740467398506.stgit@devnote2/

Fixes: ee97e5e1 ("selftests/ftrace: add fprobe test cases for VFS type "%pd" and "%pD"")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

tools/testing/selftests/ftrace/test.d/dynevent/fprobe_args_vfs.tc

 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0
 # description: Fprobe event VFS type argument
-# requires: kprobe_events "%pd/%pD":README
+# requires: dynamic_events "%pd/%pD":README "f[:[<group>/][<event>]] <func-name>[%return] [<args>]":README
+
 
 : "Test argument %pd with name for fprobe"
 echo 'f:testprobe dput name=$arg1:%pd' > dynamic_events