powerpc/powernv: Fix data type for @r in pnv_ioda_parse_m64_window()

This fixes warning reported from sparse:

  pci-ioda.c:451:49: warning: incorrect type in argument 2 (different base types)

Fixes: 262af557

 ("powerpc/powernv: Enable M64 aperatus for PHB3")
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>