net/9p: remove a comment about pref member which doesn't exist

Signed-off-by: Ryo Munakata <ryomnktml@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/9p/transport.h

@@ -34,7 +34,6 @@
  * @list: used to maintain a list of currently available transports
  * @name: the human-readable name of the transport
  * @maxsize: transport provided maximum packet size
- * @pref: Preferences of this transport
  * @def: set if this transport should be considered the default
  * @create: member function to create a new connection on this transport
  * @close: member function to discard a connection on this transport