mac80211: fix ieee80211_rx_bss_put/get imbalance

This patch fixes iee80211_rx_bss_put/get imbalance
introduced by 'mac80211: enable IBSS merging' patch.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>