ts2phc: Fix memory leak.

Each slave creates an instance of a servo.  However, when cleaning up, the
code neglected to free the servo, resulting in a memory leak.  This patch
fixes the issue by calling the appropriate method to destroy the servo.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

ts2phc_slave.c

@@ -240,6 +240,7 @@ static void ts2phc_slave_destroy(struct ts2phc_slave *slave)
 	if (ioctl(slave->fd, PTP_EXTTS_REQUEST2, &extts)) {
 		pr_err(PTP_EXTTS_REQUEST_FAILED);
 	}
+	servo_destroy(slave->servo);
 	posix_clock_close(slave->clk);
 	free(slave->name);
 	free(slave);