drm/amdgpu: handle amdgpu_cgs_create_device() errors in amd_powerplay_create()
In the Linux kernel, the following vulnerability has been resolved:

drm/amdgpu: handle amdgpu_cgs_create_device() errors in amd_powerplay_create()

Add error handling to propagate amdgpu_cgs_create_device() failures
to the caller. When amdgpu_cgs_create_device() fails, release hwmgr
and return -ENOMEM to prevent null pointer dereference.

[v1]->[v2]: Change error code from -EINVAL to -ENOMEM. Free hwmgr.