drm/amdgpu: handle VCN instances when harvesting (v2)

There may be multiple instances and only one is harvested.

v2: fix typo in commit message

Fixes: 83a0b863 ("drm/amdgpu: add judgement when add ip blocks (v2)")
Bug: drm/amd#1673


Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: James Zhu <James.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>