orinoco: Change set_tkip to use orinoco_private instead of hermes_t

hw.h does not include hermes.h, and none of the other functions
requires types from that file. Also hermes_t is a (discouraged) typedef
so we can't add a forward declaration. Therefore change this function to
use orinoco_private.

Signed-off-by: David Kilroy <kilroyd@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>