fs, omfs: add NULL terminator in the end up the token list

match_token() expects a NULL terminator at the end of the token list so
that it would know where to stop.  Not having one causes it to overrun
to invalid memory.

In practice, passing a mount option that omfs didn't recognize would
sometimes panic the system.

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Bob Copeland <me@bobcopeland.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>