hv_netvsc: Fix potential dereference of NULL pointer

The return value of netvsc_devinfo_get()
needs to be checked to avoid use of NULL
pointer in case of an allocation failure.

Fixes: 0efeea5f ("hv_netvsc: Add the support of hibernation")
Signed-off-by: Yongzhi Liu <lyz_cs@pku.edu.cn>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Link: https://lore.kernel.org/r/1652962188-129281-1-git-send-email-lyz_cs@pku.edu.cnSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/hyperv/netvsc_drv.c

@@ -2671,7 +2671,10 @@ static int netvsc_suspend(struct hv_device *dev)
 
 	/* Save the current config info */
 	ndev_ctx->saved_netvsc_dev_info = netvsc_devinfo_get(nvdev);
-
+	if (!ndev_ctx->saved_netvsc_dev_info) {
+		ret = -ENOMEM;
+		goto out;
+	}
 	ret = netvsc_detach(net, nvdev);
 out:
 	rtnl_unlock();