b43: fix the wrong assignment of status.freq in b43_rx()

commit 64e5acb09ca6b50c97299cff9ef51299470b29f2 upstream.

Use the right function to update frequency value.

If rx skb is probe response or beacon, the wrong frequency value can
cause problem that bss info can't be updated when it should be.

Fixes: 8318d78a44d4 ("cfg80211 API for channels/bitrates, mac80211
and driver conversion")
Signed-off-by: ZHAO Gang <gamerh2o@gmail.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>