flow_dissector: fix document for skb_flow_get_icmp_tci

using correct input parameter name to fix the below warning:

net/core/flow_dissector.c:242: warning: Function parameter or member 'thoff' not described in 'skb_flow_get_icmp_tci'
net/core/flow_dissector.c:242: warning: Excess function parameter 'toff' description in 'skb_flow_get_icmp_tci'
Signed-off-by: Li RongQing <lirongqing@baidu.com>
Reviewed-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/flow_dissector.c

@@ -233,7 +233,7 @@ static bool icmp_has_id(u8 type)
  * @skb: sk_buff to extract from
  * @key_icmp: struct flow_dissector_key_icmp to fill
  * @data: raw buffer pointer to the packet
- * @toff: offset to extract at
+ * @thoff: offset to extract at
  * @hlen: packet header length
  */
 void skb_flow_get_icmp_tci(const struct sk_buff *skb,