tty: Use calloc() instead of malloc() to prevent uninitialized errors.

On some platforms GCC does not zero the heap. This can lead to
serious problems, e.g., tty->pid may be non-zero while never
having been started.

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

tty.c

@@ -71,7 +71,7 @@ int tty_register(char *line)
 	entry = tty_find(dev);
 	if (!entry) {
 		insert = 1;
-		entry = malloc(sizeof(*entry));
+		entry = calloc(1, sizeof(*entry));
 		if (!entry)
 			return errno = ENOMEM;
 	}