drm/nouveau/kms/nv50-: fix file release memory leak

When using single_open() for opening, single_release() should be
called, otherwise the 'op' allocated in single_open() will be leaked.

Fixes: 12885ecb ("drm/nouveau/kms/nvd9-: Add CRC support")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Karol Herbst <kherbst@redhat.com>
Signed-off-by: Karol Herbst <kherbst@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210911075023.3969054-1-yangyingliang@huawei.comSigned-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/nouveau/dispnv50/crc.c

@@ -704,6 +704,7 @@ static const struct file_operations nv50_crc_flip_threshold_fops = {
 	.open = nv50_crc_debugfs_flip_threshold_open,
 	.read = seq_read,
 	.write = nv50_crc_debugfs_flip_threshold_set,
+	.release = single_release,
 };
 
 int nv50_head_crc_late_register(struct nv50_head *head)