drm/amdgpu: handle bo size 0 in amdgpu_bo_create_kernel_at (v2)

Just return early to match other bo_create functions.

v2: check if the bo_ptr is NULL rather than checking the size.
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com> (v1)
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -374,6 +374,9 @@ int amdgpu_bo_create_kernel_at(struct amdgpu_device *adev,
 	if (r)
 		return r;
 
+	if ((*bo_ptr) == NULL)
+		return 0;
+
 	/*
 	 * Remove the original mem node and create a new one at the request
 	 * position.