PCI: acpiphp_ibm: Avoid uninitialized variable reference

If ibm_get_table_from_acpi() fails then "table" isn't initialized.  Check
for failure so we don't reference "table" unless it's been initialized.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>