Fix PCIeDevice redfish validator failure

Specify correct  interface for getSubTreePaths in getPCIeDeviceList.

This commit addresses a Redfish validator failure that occurred after a
previous commit.
'''
https://github.com/openbmc/bmcweb/commit/94c3a10b94c3ce063d6c1aed3a597f0d524594d5


'''
Both the inventory path and interface were incorrect, and the inventory
path was fixed in the previous commit. This commit fixes the interface
in the getSubTreePaths function to ensure that it returns the correct
PCIeDevice list. Without the correct interface, the function was
returning incorrect devices, which was causing the Redfish validator
failure.

Tested: Validator passed for PCIeDevice

Change-Id: Iab6a26ee0dd933be6cf371bdd13e5d10d6d10efa
Signed-off-by: Lakshmi Yadlapati <lakshmiy@us.ibm.com>