powerpc/44x: Fix UART clocks on 440SPe

The code to fixup the serial ports on 440SPe uses the incorrect
addresses for these. This fixes it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Josh Boyer <jwboyer@linux.vnet.ibm.com>