drm/amd: Fix unbind/rebind for VCN 4.0.5

drm/amd: Fix unbind/rebind for VCN 4.0.5

Unbinding amdgpu has no problems, but binding it again leads to an
error of sysfs file already existing.  This is because it wasn't
actually cleaned up on unbind.  Add the missing cleanup step.

Fixes: 547aad32edac ("drm/amdgpu: add VCN4 ip block support")
Signed-off-by: Mario Limonciello (AMD) <superm1@kernel.org>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d717e62e9b6ccff0e3cec78a58dfbd00858448b3)
Cc: stable@vger.kernel.org