PCI: pcie portdriver: initialize returned value

The pcie protdrv status can be returned uninitialized,
if there are no children under a device. This leads to
bad responses downstream. Fix this.

Signed-off-by: Linas Vepstas <linas@austin.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>