powerpc/powernv: Simplify pnv_ioda_configure_pe()

Nested if statements are always bad and the patch avoids one by
checking PHB type and bail in advance if necessary.

Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>