amdgpu: make sure to set CLOEXEC on duplicated FDs

Otherwise we leak file descriptors into child processes.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-and-Tested-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>