net: sctp: simplify sctp_get_port

No need to have an extra ret variable when we directly can return
the value of sctp_get_port_local().

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>