sctp: fix sparse warning for sctp_init_cause_fixed

Fix the following sparse warning:
	* symbol 'sctp_init_cause_fixed' was not declared. Should it be
	  static?

Signed-off-by: Ioan Orghici <ioanorghici@gmail.com>
Acked-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>