sctp: Fix use of uninitialized pointer

Introduced by c4492586 (sctp: Add address type check while process
paramaters of ASCONF chunk):

net/sctp/sm_make_chunk.c: In function 'sctp_process_asconf':
net/sctp/sm_make_chunk.c:2828: warning: 'addr_param' may be used uninitialized in this function
net/sctp/sm_make_chunk.c:2828: note: 'addr_param' was declared here

Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>