When checking for the band, use channel->band.

Change ath5k_hw_nic_wakeup() and ath5k_channel_ok() to take
ieee80211_channel.  Change ath5k_hw_radio_revision() to take
ieee80211_band.
Signed-off-by: Pavel Roskin <proski@gnu.org>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com>
Acked-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>