wl12xx: Fix potential incorrect band in rx-status

The rx-status passed to mac80211 along with each received frame contains the
band on which the frame was received. Under certain circumstances, this band
information may be incorrect, causing in worst case a WARNING from mac80211,
and causes the received frame to be dropped.

This scenario mainly occurs when performing connected-mode scans, when the
received scan results are from the other band than the one currently
associated to.

[Since desc_band doesn't exist anymore, use status->band in the later
call to ieee80211_channel_to_frequency() to fix compilation -- Luca]

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>