drm/i915/gvt: fix the usage of ww lock in gvt scheduler.

As the APIs related to ww lock in i915 was changed recently, the usage of
ww lock in GVT-g scheduler needs to be changed accrodingly. We noticed a
deadlock when GVT-g scheduler submits the workload to i915. After some
investigation, it seems the way of how to use ww lock APIs has been
changed. Releasing a ww now requires a explicit i915_gem_ww_ctx_fini().

Fixes: 67f1120 ("drm/i915/gvt: Introduce per object locking in GVT scheduler.")
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Zhi A Wang <zhi.a.wang@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210826143834.25410-1-zhi.a.wang@intel.com
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/scheduler.c

@@ -576,7 +576,7 @@ static int prepare_shadow_batch_buffer(struct intel_vgpu_workload *workload)
 
 			/* No one is going to touch shadow bb from now on. */
 			i915_gem_object_flush_map(bb->obj);
-			i915_gem_object_unlock(bb->obj);
+			i915_gem_ww_ctx_fini(&ww);
 		}
 	}
 	return 0;
@@ -630,7 +630,7 @@ static int prepare_shadow_wa_ctx(struct intel_shadow_wa_ctx *wa_ctx)
 		return ret;
 	}
 
-	i915_gem_object_unlock(wa_ctx->indirect_ctx.obj);
+	i915_gem_ww_ctx_fini(&ww);
 
 	/* FIXME: we are not tracking our pinned VMA leaving it
 	 * up to the core to fix up the stray pin_count upon