powerpc/powernv/ioda: Fix TCE invalidate to work in real mode again

Commit fd141d1a ("powerpc/powernv/pci: Rework accessing the TCE
invalidate register") broke TCE invalidation on IODA2/PHB3 for real
mode.

This makes invalidate work again.

Fixes: fd141d1a ("powerpc/powernv/pci: Rework accessing the TCE invalidate register")
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>