tomoyo: use vsnprintf() properly

Idiomatic way to find how much space sprintf output would take is
	len = snprintf(NULL, 0, ...) + 1;
Once upon a time there'd been libc implementations that blew chunks
on that and somebody had come up with the following "cute" trick:
	len = snprintf((char *) &len, 1, ...) + 1;
for doing the same.  However, that's unidiomatic, harder to follow
*and* any such libc implementation would violate both C99 and POSIX
(since 2001).
	IOW, this kludge is best buried along with such libc implementations,
nevermind getting cargo-culted into newer code.  Our vsnprintf() does not
suffer that braindamage, TYVM.

Acked-by: Tetsuo Handa <[email protected]>
Signed-off-by: Al Viro <[email protected]>

security/tomoyo/audit.c

@@ -423,7 +423,7 @@ void tomoyo_write_log(struct tomoyo_request_info *r, const char *fmt, ...)
 	int len;
 
 	va_start(args, fmt);
-	len = vsnprintf((char *) &len, 1, fmt, args) + 1;
+	len = vsnprintf(NULL, 0, fmt, args) + 1;
 	va_end(args);
 	va_start(args, fmt);
 	tomoyo_write_log2(r, len, fmt, args);

security/tomoyo/common.c

@@ -2057,7 +2057,7 @@ int tomoyo_supervisor(struct tomoyo_request_info *r, const char *fmt, ...)
 	bool quota_exceeded = false;
 
 	va_start(args, fmt);
-	len = vsnprintf((char *) &len, 1, fmt, args) + 1;
+	len = vsnprintf(NULL, 0, fmt, args) + 1;
 	va_end(args);
 	/* Write /sys/kernel/security/tomoyo/audit. */
 	va_start(args, fmt);