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

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

drivers/gpu/drm/amd/amdkfd/kfd_iommu.c: In function kfd_iommu_device_init:
drivers/gpu/drm/amd/amdkfd/kfd_iommu.c:65:30: warning: variable top_dev set but not used [-Wunused-but-set-variable]
Reported-by: Hulk Robot <hulkci@huawei.com>
Fixes: 1ae99eab ("drm/amdkfd: Initialize HSA_CAP_ATS_PRESENT capability in topology codes")
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_iommu.c

@@ -62,9 +62,6 @@ int kfd_iommu_device_init(struct kfd_dev *kfd)
 	struct amd_iommu_device_info iommu_info;
 	unsigned int pasid_limit;
 	int err;
-	struct kfd_topology_device *top_dev;
-
-	top_dev = kfd_topology_device_by_id(kfd->id);
 
 	if (!kfd->device_info->needs_iommu_device)
 		return 0;