qcacld-3.0: Acquire sap context before access

Fix potential race condition issue when the sap_context
of adapter is null and it is accessed in work queue -
 __policy_mgr_check_sta_ap_concurrent_ch_intf.
To acquire/release the "sap_context" by get/put API.

Change-Id: I91dacc6d45c377840f7d30f2f9ff902f53ccd8e8
CRs-Fixed: 2592524

core/sap/src/sap_module.c

@@ -3164,6 +3164,10 @@ qdf_freq_t wlansap_get_chan_band_restrict(struct sap_context *sap_ctx)
 	enum reg_wifi_band sap_band;
 	enum band_info band;
 
+	if (!sap_ctx) {
+		sap_err("sap_ctx NULL parameter");
+		return 0;
+	}
 	if (cds_is_driver_recovering())
 		return 0;