nl80211: Derive frequency for BSSes other than the first

nl80211: Derive frequency for BSSes other than the first

Commit e4fb21676972952b5434e8c2a049e239d457abe6 moved frequency
storage from driver struct to bss struct and is assigned in
wpa_driver_nl80211_set_freq. As this wpa_driver_nl80211_set_freq is
triggered only on the first_bss, bss->freq for other BSSes is never
being set to the correct value. This sends MLME frames on frequency zero
(initialized value of freq) for BSSes other than the first.

To fix this derive frequency value from first_bss.

Signed-off-by: Yogesh Ashok Powar <yogeshp@marvell.com>