lssu: fix format-security warning at lssu_print_header()

Fix the following gcc warning on some platforms:

 lssu.c: In function 'lssu_print_header':
 lssu.c:127:2: warning: format not a string literal and no format arguments [-Wformat-security]
   printf(lssu_format[disp_mode].header);
   ^

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>