HID: steam: Refactor registration

In the Linux kernel, the following vulnerability has been resolved: HID: steam: Refactor registration This refactors and simplifies the registration/unregistration flow. Since we now only perform registration when the client isn't opened anymore, the logic for handling that can be removed, and the rest of the function streamlined. We also remove the previous assumption that we have a serial number to show we're registered, replacing it with a single purpose boolean. In a previous refactor the code for unregistering a battery if later registration steps failed was accidentally left out. As a result, a lingering power_supply object could get left over after the steam object was torn down. This is also fixed here.

Where it's fixed