nfc: constify pointer to nfc_vendor_cmd

Neither the core nor the drivers modify the passed pointer to struct
nfc_vendor_cmd, so make it a pointer to const for correctness and
safety.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/nfc/netlink.c b/net/nfc/netlink.c
index 722f7ef..70467a8 100644
--- a/net/nfc/netlink.c
+++ b/net/nfc/netlink.c
@@ -1531,7 +1531,7 @@ static int nfc_genl_vendor_cmd(struct sk_buff *skb,
 			       struct genl_info *info)
 {
 	struct nfc_dev *dev;
-	struct nfc_vendor_cmd *cmd;
+	const struct nfc_vendor_cmd *cmd;
 	u32 dev_idx, vid, subcmd;
 	u8 *data;
 	size_t data_len;