mac80211: tkip.c fold ieee80211_gen_rc4key into its one caller

Also change the arguments of the phase1, 2 key mixing to take
a pointer to the encrytion key and the tkip_ctx in the same
order.

Do the dereference of the encryption key in the callers.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>