[POWERPC] Celleb: bug fix caused by not casting pointer types

This fixes a bug caused by changes of pointer type in
commit f1fda895

.

hose->cfg_addr type is "volatile unsigned int __iomem *", so
"hose->cfg_addr + X" will not make an intended address.

This patch also adds comments for usage of cfg_addr and cfg_data in
pci_controller structure.  We use them in irregular way, and the
original code is short of explanations about them.

Signed-off-by: Kou Ishizaki <kou.ishizaki@toshiba.co.jp>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>