serial: atmel: fix compiler warning on address cast

Turning on KVM and LPAE support on top of a multi_v7_defconfig will
produce a compiler warning in the Atmel serial driver:
drivers/tty/serial/atmel_serial.c: In function 'atmel_verify_port':
drivers/tty/serial/atmel_serial.c:2299:6: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]
  if ((void *)port->mapbase != ser->iomem_base)
      ^

Fix that by using the cast on the right hand side instead, as similar
code already does in other drivers.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/atmel_serial.c

@@ -2302,7 +2302,7 @@ static int atmel_verify_port(struct uart_port *port, struct serial_struct *ser)
 		ret = -EINVAL;
 	if (port->uartclk / 16 != ser->baud_base)
 		ret = -EINVAL;
-	if ((void *)port->mapbase != ser->iomem_base)
+	if (port->mapbase != (unsigned long)ser->iomem_base)
 		ret = -EINVAL;
 	if (port->iobase != ser->port)
 		ret = -EINVAL;