Add fused location provider to real provider list

During testing it's possible to mock a location provider, but the fused
location provider wasn't being inserted into the "mRealProviders" map so
when the fused location provider was unmocked, it would disappear
permanently from the list until the next reboot.

Bug: 6949478
Change-Id: I4993aa7fbbd21cea16bdbf2722d637c909b1cd73