selftests/ftrace: Fix eprobe syntax test case to check filter support

Fix eprobe syntax test case to check whether the kernel supports the filter
on eprobe for filter syntax test command. Without this fix, this test case
will fail if the kernel supports eprobe but doesn't support the filter on
eprobe.

Link: https://lore.kernel.org/all/167309834742.640500.379128668288448035.stgit@devnote3/



Fixes: 9e14bae7 ("selftests/ftrace: Add eprobe syntax error testcase")
Cc: stable@vger.kernel.org
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>