net/flow_dissector: remove unexist field description

@thoff has moved to struct flow_dissector_key_control.

Fixes: 42aecaa9 ("net: Get skb hash over flow_keys structure")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/flow_dissector.h

@@ -33,7 +33,6 @@ enum flow_dissect_ret {
 
 /**
  * struct flow_dissector_key_basic:
- * @thoff: Transport header offset
  * @n_proto: Network header protocol (eg. IPv4/IPv6)
  * @ip_proto: Transport header protocol (eg. TCP/UDP)
  */