[RPC]: Kill bogus kmap in krb5

While I was going through the crypto users recently, I noticed this
bogus kmap in sunrpc.  It's totally unnecessary since the crypto
layer will do its own kmap before touching the data.  Besides, the
kmap is throwing the return value away.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>