net: sctp: minor: remove variable in sctp_init_sock

It's only used at this one time, so we could remove it as well.
This is valid and also makes it more explicit/obvious that in case
of error the sp->ep is NULL here, i.e. for the sctp_destroy_sock()
check that was recently added.

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