PCI: rpaphp: refactor tail call to rpaphp_register_slot()

Eliminate the tail call to rpaphp_register_slot() 
by placing it in the caller. This will help later
dis-entanglement.

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>