drm/amdgpu: Use struct_size() helper in kmalloc()

Make use of the new struct_size() helper instead of the offsetof() idiom.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_amdkfd_gpuvm.c

@@ -239,8 +239,7 @@ static int amdgpu_amdkfd_remove_eviction_fence(struct amdgpu_bo *bo,
 	if (!old)
 		return 0;
 
-	new = kmalloc(offsetof(typeof(*new), shared[old->shared_max]),
-		      GFP_KERNEL);
+	new = kmalloc(struct_size(new, shared, old->shared_max), GFP_KERNEL);
 	if (!new)
 		return -ENOMEM;