PCI: rpaphp: Use pcibios_remove_pci_devices() symmetrically

At first blush, the disable_slot() routine does not look
at all like its symmetric with the enable_slot() routine;
as it seems to call a very different set of routines.
However, this is easily fixed: pcibios_remove_pci_devices()
does the right thing.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Cc: John Rose <johnrose@austin.ibm.com>
Signed-off-by: Kristen Carlson Accardi <kristen.c.accardi@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>