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 <[e-mail]>
Acked-by: Vlad Yasevich <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/sctp/sm_make_chunk.c

···
  * abort chunk.  Differs from sctp_init_cause in that it won't oops
  * if there isn't enough space in the op error chunk
  */
-int sctp_init_cause_fixed(struct sctp_chunk *chunk, __be16 cause_code,
+static int sctp_init_cause_fixed(struct sctp_chunk *chunk, __be16 cause_code,
 		      size_t paylen)
 {
 	sctp_errhdr_t err;