fcntl: Don't set si_code to SI_SIGIO when sig == SIGPOLL

When fixing things to avoid ambiguous cases I had a thinko
and included SIGPOLL/SIGIO in with all of the other signals
that have signal specific si_codes.  Which is completely wrong.

Fix that.

Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>