qcacld-3.0: Check NULL pointer of roam_profile

qcacld-3.2 to qcacld-3.1 propagation

__wlan_hdd_cfg80211_get_key was invoked when unloading driver.
SAP ctx had been freed at this time.wlan_sap_get_roam_profile will
return NULL.

Check NULL pointer before use roam_profile.

Change-Id: If1f11f0fb7027a6af4e3242fe9af722740d32850
CRs-Fixed: 2162395