sctp: replace seq_printf with seq_puts

Fixes checkpatch warning:
"WARNING: Prefer seq_puts to seq_printf"

Signed-off-by: Michele Baldessari <michele@acksyn.org>
Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>