qcacld-3.0: Fix possible null pointer dereference

Fix a possible null pointer dereference in wlan_hdd_cfg80211_ll_stats_get
and _wlan_hdd_cfg80211_get_station if global qdf device context becomes
null.

Change-Id: I02362ae2c60769a562acc42805bd8c4ccac0e887
CRs-fixed: 2536319
1 file changed