MAINTAINERS: add myself as FIPS140 standalone module maintainer

As a gesture of accepting responsibility for the FIPS140 code, add
myself to MAINTAINERS. This is not meant to override or supersede
crypto maintainers and in fact I'd expect any FIPS140-related patches
to still go through the crypto tree(s). I encourage others with an
interest in the long term maintenance of the FIPS140 code to add
themselves to this entry as well.

Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>