drm/amdkfd: Remove unessary void pointer cast

kmalloc() returns a void pointer - no need to cast it in
drivers/gpu/drm/amd/amdkfd/kfd_process.c::kfd_process_destroy_delayed()

Signed-off-by: Firo Yang <firogm@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@amd.com>