CVE-2026-98779: drm/amdgpu: fix ACP MFD device leak on init failure

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

drm/amdgpu: fix ACP MFD device leak on init failure

acphwinit() registers ACP child devices with mfdadddevices() before attaching them to the ACP power domain and initializing the hardware.

If attaching a child to the power domain fails, or if the ACP reset or clock enable operation times out, the failure path frees only the source cell, resource, and platform-data allocations. The child platform devices already registered by mfdadddevices() remain registered and are never released.

Remove the children from the power domain and unregister the MFD devices on failures that occur after mfdadddevices() succeeds. Keep mfdadddevices() failures on the existing cleanup path since the MFD core already rolls back partially registered children itself.

The issue was identified by a static analysis tool I developed and confirmed by manual review.

(cherry picked from commit 63da68d6a2279ec945581c990c5a59a5ae8b5560)