Patch from Deepak Saxena

There seems to be a typo that has creeped into
include/asm/arch-ixp4xx/ixp4xx-regs.h. IXP4XX_EXP_CFG_BASE_VIRT and
IXP4XX_PCI_CFG_BASE_VIRT were both defined to the same value. The patch
changes PCI_CFG_BASE_VIRT to the value in the memory map comment.
  

Signed-off-by: Deepak Saxena
Signed-off-by: Russell King