iscsi_top: restore old delay value if scanf fails

	struct spdk_trace_history *history;

	uint64_t		tasks_done, last_tasks_done[SPDK_TRACE_MAX_LCORE];

	int			delay, history_fd, i, quit, rc;

	int			delay, old_delay, history_fd, i, quit, rc;

	int			tasks_done_delta, tasks_done_per_sec;

	int			total_tasks_done_per_sec;

	struct timeval		timeout;

			switch (ch) {

			case 'd':

				printf("Enter num seconds to delay (1-10): ");

				old_delay = delay;

				rc = scanf("%d", &delay);

				if (rc != 1) {

					break;

					fprintf(stderr, "Illegal delay value\n");

					delay = old_delay;

				} else if (delay < 1 || delay > 10) {

					delay = 1;

				}