Another problem pointed out by clang

Using format specifiers without arguments in printf is still bad.

openbox/debug.c:105:18: warning: format string is not a string literal (potentially insecure)
    fprintf(out, log_domain);
                 ^~~~~~~~~~
openbox/debug.c:107:18: warning: format string is not a string literal (potentially insecure)
    fprintf(out, level);
                 ^~~~~
openbox/debug.c:109:18: warning: format string is not a string literal (potentially insecure)
    fprintf(out, message);
                 ^~~~~~~