selftests/ftrace: Fix to use remount when testing mount GID option

selftests/ftrace: Fix to use remount when testing mount GID option

commit 159ca65c42d90d5ab98fc31b708b12c0be2c26e0 upstream.

Fix mount_options.tc to use remount option to mount the tracefs.
Since the current implementation does not umount the tracefs,
this test always fails because of -EBUSY error.
Using remount option will allow us to change the mount option.

Link: https://lore.kernel.org/r/173625186741.1383744.16707876180798573039.stgit@devnote2
Fixes: 8b55572e5180 ("tracing/selftests: Add tracefs mount options test")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>