drm/amdgpu: fix double free err_addr pointer warnings

In the Linux kernel, the following vulnerability has been resolved: drm/amdgpu: fix double free err_addr pointer warnings In amdgpu_umc_bad_page_polling_timeout, the amdgpu_umc_handle_bad_pages will be run many times so that double free err_addr in some special case. So set the err_addr to NULL to avoid the warnings.