drm/vc4: Use vc4_perfmon_find()

Similar to commit f2a4bcb ("drm/v3d: Use v3d_perfmon_find()"),
replace the open-coded `vc4_perfmon_find()` with the real thing.

Cc: Christian Gmeiner <cgmeiner@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Juan A. Suarez <jasuarez@igalia.com>
Reviewed-by: Christian Gmeiner <cgmeiner@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241004123817.890016-1-mcanal@igalia.com

drivers/gpu/drm/vc4/vc4_perfmon.c

@@ -236,11 +236,7 @@ int vc4_perfmon_get_values_ioctl(struct drm_device *dev, void *data,
 		return -ENODEV;
 	}
 
-	mutex_lock(&vc4file->perfmon.lock);
-	perfmon = idr_find(&vc4file->perfmon.idr, req->id);
-	vc4_perfmon_get(perfmon);
-	mutex_unlock(&vc4file->perfmon.lock);
-
+	perfmon = vc4_perfmon_find(vc4file, req->id);
 	if (!perfmon)
 		return -EINVAL;