Make sure GRID_NAME is updated every time it changes.

Bore it was only updated when the device was innitialized,
but other changes to the IDP would not udpate the GRID_NAME pref.

Fix: 380954618
Test: NA
Flag: com.android.launcher3.one_grid_specs
Change-Id: I4fa73a4b838c0d0c7c1c88ea91c62ac8ae6676b7