drm/amdgpu: disble vblank when unloading sriov driver

disble vblank in dce_vitual_crtc_commit(), which is skipped
under sriov before

Reviewed-by: Emily Deng <[e-mail]>
Signed-off-by: Jiawei <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 {
 	struct amdgpu_crtc *amdgpu_crtc = to_amdgpu_crtc(crtc);
 
-	dce_virtual_crtc_dpms(crtc, DRM_MODE_DPMS_OFF);
+	drm_crtc_vblank_off(crtc);
 
+	amdgpu_crtc->enabled = false;
 	amdgpu_crtc->pll_id = ATOM_PPLL_INVALID;
 	amdgpu_crtc->encoder = NULL;
 	amdgpu_crtc->connector = NULL;