hv_netvsc: Fix dereference of nvdev before check

Passes static analysis by Smatch.
Signed-off-by: NAndrew Schwartzmeyer <andschwa@microsoft.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/hyperv/netvsc_drv.c

@@ -777,14 +777,17 @@ static int netvsc_set_channels(struct net_device *net,
 	struct hv_device *dev = net_device_ctx->device_ctx;
 	struct netvsc_device *nvdev = hv_get_drvdata(dev);
 	struct netvsc_device_info device_info;
-	const u32 num_chn = nvdev->num_chn;
-	const u32 max_chn = min_t(u32, nvdev->max_chn, num_online_cpus());
+	u32 num_chn;
+	u32 max_chn;
 	int ret = 0;
 	bool recovering = false;
 
 	if (!nvdev || nvdev->destroy)
 		return -ENODEV;
 
+	num_chn = nvdev->num_chn;
+	max_chn = min_t(u32, nvdev->max_chn, num_online_cpus());
+
 	if (nvdev->nvsp_version < NVSP_PROTOCOL_VERSION_5) {
 		pr_info("vRSS unsupported before NVSP Version 5\n");
 		return -EINVAL;