Change use of default sub to default data sub in GnssLocationProvider

An earlier CL ag/5462517 (as part of fix for b/118770440) updated
GnssLocationProvider to load config from default data subscription.

This CL addresses comment #11 in the b/119663753. Replaced couple of
places where default sub is used instead of default data sub as first
preference.

Bug: 119663753
Test: Existing tests pass on a single SIM device
Change-Id: Ic47b0743c00c51a49e1dd6e1cfb5d396b2289d0f