char/cadence_uart: Add missing uart_update_state

This should be rechecked on bus write accesses as such accesses may
change the underlying state that generates the interrupt. Particular
relevant for when the guest touches the interrupt status or mask.
Signed-off-by: NPeter Crosthwaite <peter.crosthwaite@xilinx.com>
Message-id: 1c250cd61b7b8de492fbc8b79b8370958a56d83b.1388626249.git.peter.crosthwaite@xilinx.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/char/cadence_uart.c

@@ -403,6 +403,7 @@ static void uart_write(void *opaque, hwaddr offset,
         uart_parameters_setup(s);
         break;
     }
+    uart_update_status(s);
 }
 
 static uint64_t uart_read(void *opaque, hwaddr offset,