sctp: remove redundant assignment when call sctp_get_port_local

There are more parentheses in if clause when call sctp_get_port_local
in sctp_do_bind, and redundant assignment to 'ret'. This patch is to
do cleanup.

Signed-off-by: Mao Wenan <maowenan@huawei.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Acked-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>