tty: xuartps: Keep lock for whole ISR

The RX path in the interrupt handler released a lock unnecessarily.
Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/xilinx_uartps.c

@@ -265,9 +265,7 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id)
 			uart_insert_char(port, isrstatus, CDNS_UART_IXR_OVERRUN,
 					data, status);
 		}
-		spin_unlock(&port->lock);
 		tty_flip_buffer_push(&port->state->port);
-		spin_lock(&port->lock);
 	}
 
 	/* Dispatch an appropriate handler */