tty: serial: xilinx_uartps: Supply description for missing member 'cts_override'

Fixes the following W=1 kernel build warning(s):

drivers/tty/serial/xilinx_uartps.c:205: warning: Function parameter or member 'cts_override' not described in 'cdns_uart'

Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jiri Slaby <[e-mail]>
Cc: Michal Simek <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/xilinx_uartps.c

···
  * @baud:		Current baud rate
  * @clk_rate_change_nb:	Notifier block for clock changes
  * @quirks:		Flags for RXBS support.
+ * @cts_override:	Modem control state override
  */
 struct cdns_uart {
 	struct uart_port	*port;