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 acp_hw_init() registers ACP child devices with mfd_add_devices() 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 mfd_add_devices() remain registered and are never released. Remove the children from the power domain and unregister the MFD devices on failures that occur after mfd_add_devices() succeeds. Keep mfd_add_devices() 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)