qcacld-3.0: Avoid NULL dereference in hdd_init_qdf_ctx()

Currently hdd_init_qdf_ctx() calls cds_get_context() to retrieve the
QDF Device context, and then writes into the context without
validating the pointer.  Add logic to validate the pointer before
using it.

Change-Id: Ib427d1348b3ff5b13689e24f69e4606f23ea767c
CRs-Fixed: 1042043

core/hdd/src/wlan_hdd_driver_ops.c

@@ -294,6 +294,11 @@ void hdd_init_qdf_ctx(struct device *dev, void *bdev,
 {
 	qdf_device_t qdf_dev = cds_get_context(QDF_MODULE_ID_QDF_DEVICE);
 
+	if (!qdf_dev) {
+		hdd_err("Invalid QDF device");
+		return;
+	}
+
 	qdf_dev->dev = dev;
 	qdf_dev->drv_hdl = bdev;
 	qdf_dev->bus_type = bus_type;