Only check dbFile to decide if grid migration is needed

Fix: 234847755
Test: With a modified local build, when changing display config to swap between same grid:
- When dbFile is same but device type is different, no migration is performed
- When both dbFile and device type are different, migration is performed properly
Test: Grid migration through Wallpaper & Styles still works properly

Change-Id: Ie7429a7d59c135ba47061cae21c40b8d8af7188a