drivers/serial/mpc52xx_uart.c: Use UPIO_MEM rather than SERIAL_IO_MEM

As in the commit 9b4a1617

, use UPIO_MEM
rather than SERIAL_IO_MEM.  Both have the same value.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@has_sc@
@@

#include <linux/serial_core.h>

@depends on has_sc@
@@

- SERIAL_IO_MEM
+ UPIO_MEM
// </smpl>

Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>