its-g5: ath9k: Fix OCB handling

Signed-off-by: Rostislav Lisovy <rostislav.lisovy@fel.cvut.cz>
its-g5: Not smart to use a pointer to the data in local scope in long term

Signed-off-by: Rostislav Lisovy <rostislav.lisovy@fel.cvut.cz>
its-g5: Avoid multiple consecutive calls to ocb_join

Signed-off-by: Rostislav Lisovy <rostislav.lisovy@fel.cvut.cz>