tomoyo: add format attributes to functions

Format attributes on functions taking format string can help compilers
detect argument type or count mismatches.

Please the compiler when building with W=1:

    security/tomoyo/audit.c: In function ‘tomoyo_init_log’:
    security/tomoyo/audit.c:290:9: error: function ‘tomoyo_init_log’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
      290 |         vsnprintf(buf + pos, len - pos, fmt, args);
          |         ^~~~~~~~~
    security/tomoyo/audit.c: In function ‘tomoyo_write_log2’:
    security/tomoyo/audit.c:376:9: error: function ‘tomoyo_write_log2’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
      376 |         buf = tomoyo_init_log(r, len, fmt, args);
          |         ^~~
    security/tomoyo/common.c: In function ‘tomoyo_addprintf’:
    security/tomoyo/common.c:193:9: error: function ‘tomoyo_addprintf’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
      193 |         vsnprintf(buffer + pos, len - pos - 1, fmt, args);
          |         ^~~~~~~~~

Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>