powerpc/powernv: Fix corrupted PE allocation bitmap on releasing PE

In pnv_ioda_free_pe(), the PE object (including the associated PE
number) is cleared before resetting the corresponding bit in the
PE allocation bitmap. It means PE#0 is always released to the bitmap
wrongly.

This fixes above issue by caching the PE number before the PE object
is cleared.

Fixes: 1e916772 ("powerpc/powernv: Use PE instead of number during setup and release"
Cc: stable@vger.kernel.org # v4.7+
Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>