fru: Fix retrieval of bifurcation data from Entity Manager

Summary:
1. Adjust the functions used to get the bifurcation data from entity
   manager to use the correct type.
```
Failed to get deviceLanes: sd_bus_message_read_basic fundamental: System.Error.ENXIO: No such device or address
```
2. Ensure the data structure updated is the long term one, and not just
   a temporary copy.

Tested:
Exceptions are no longer thrown when running these function
when the corresponding DBus properties exist. The EM bifurcation data
is present in the final binary.
```
// Before, value would be set to 00 indicating not present
root@platform30:~# hexdump -C /run/pcie0.cfg
00000000  08 00 02 08 08 02 08 08  02 01 04 02 08 08 02 08  |................|
00000010  08 02 08 08 02 01 04                              |.......|
00000017
// After, value is set to x16 as specified in the EM json
root@platform30:~# hexdump -C /run/pcie0.cfg
00000000  08 01 10 02 08 08 02 08  08 02 01 04 02 08 08 02  |................|
00000010  08 08 02 08 08 02 01 04                           |........|
00000018
```

Google-Bug-Id: 435526024
Change-Id: I4f84290596672ff22aa9cb64e8a978f61d501282
Signed-off-by: Kyle Nieman <kyle.nieman@fii-na.corp-partner.google.com>