CVE-2026-98945: HID: steam: Rearrange teardown sequence

In the Linux kernel, the following vulnerability has been resolved:

HID: steam: Rearrange teardown sequence

This fixes a narrow window during the teardown sequence where callbacks could still be scheduled during cleanup that would then have a dangling pointer to the now-freed steam struct.

This also puts work canceling for rumble and mode switch in steamunregister, as that shouldn't persist while the client hdev is open.