tty: Clean up completely if switching vt fails

The code under the "err" label closes the file descriptor and frees the
allocated memory.

src/tty.c

@@ -174,7 +174,7 @@ tty_create(struct weston_compositor *compositor, tty_vt_func_t vt_func,
 		if (ioctl(tty->fd, VT_ACTIVATE, tty->vt) < 0 ||
 		    ioctl(tty->fd, VT_WAITACTIVE, tty->vt) < 0) {
 			weston_log("failed to swtich to new vt\n");
-			return NULL;
+			goto err;
 		}
 	}