powerpc/eeh: Don't collect logs on PE with blocked config space

When the PE's config space is marked as blocked, PCI config read
requests always return 0xFF's. It's pointless to collect logs in
this case.

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