drm/i915/gem: Rework error handling in default_engines

Since free_engines works for partially constructed engine sets, we can
use the usual goto pattern.
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210708154835.528166-18-jason@jlekstrand.net

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -366,7 +366,7 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
 {
 	const struct intel_gt *gt = &ctx->i915->gt;
 	struct intel_engine_cs *engine;
-	struct i915_gem_engines *e;
+	struct i915_gem_engines *e, *err;
 	enum intel_engine_id id;
 
 	e = alloc_engines(I915_NUM_ENGINES);
@@ -384,18 +384,21 @@ static struct i915_gem_engines *default_engines(struct i915_gem_context *ctx)
 
 		ce = intel_context_create(engine);
 		if (IS_ERR(ce)) {
-			__free_engines(e, e->num_engines + 1);
-			return ERR_CAST(ce);
+			err = ERR_CAST(ce);
+			goto free_engines;
 		}
 
 		intel_context_set_gem(ce, ctx);
 
 		e->engines[engine->legacy_idx] = ce;
-		e->num_engines = max(e->num_engines, engine->legacy_idx);
+		e->num_engines = max(e->num_engines, engine->legacy_idx + 1);
 	}
-	e->num_engines++;
 
 	return e;
+
+free_engines:
+	free_engines(e);
+	return err;
 }
 
 void i915_gem_context_release(struct kref *ref)