tty: serial: 8250_core.c Bug fix for Exar chips.

The sleep function was updated to put the serial port to sleep only when necessary.
This appears to resolve the errant behavior of the driver as described in
Kernel Bug 61961 – "My Exar Corp. XR17C/D152 Dual PCI UART modem does not
work with 3.8.0".
Signed-off-by: NMichael Welling <mwelling@ieee.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_core.c

@@ -555,7 +555,7 @@ static void serial8250_set_sleep(struct uart_8250_port *p, int sleep)
 	 */
 	if ((p->port.type == PORT_XR17V35X) ||
 	   (p->port.type == PORT_XR17D15X)) {
-		serial_out(p, UART_EXAR_SLEEP, 0xff);
+		serial_out(p, UART_EXAR_SLEEP, sleep ? 0xff : 0);
 		return;
 	}