drm/amdkfd: remove set but not used variable 'pdd'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c: In function restore_process_worker:
drivers/gpu/drm/amd/amdgpu/../amdkfd/kfd_process.c:949:29: warning:
 variable pdd set but not used [-Wunused-but-set-variable]

It is not used since
commit 5b87245f ("drm/amdkfd: Simplify kfd2kgd interface")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>