sctp: remove useless err from sctp_association_init

This patch is to remove the unnecessary temporary variable 'err' from
sctp_association_init.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>