qcacld-3.0: Relocate fetching of hdd_ctx to avoid stale pointer

In the function hdd_driver_unload, the hdd_ctx is fetched at the
beginning before the dsc_wait_for_trans. In the scenario where this
wait_for_trans is active and in the other thread (for example when
wlan_pld_remove and rmmod run in parallel) the hdd_ctx is invalidated,
the local copy of the pointer becomes stale. Accessing this stale
pointer leads to page fault.

Do not fetch the hdd_ctx before waiting for dsc trans. Rather fetch it
just before where it is actually used.

Change-Id: Ia5524c7a2af8ff2e976a6f1d3e87f2f374fdc371
CRs-Fixed: 2720714

core/hdd/src/wlan_hdd_main.c

@@ -15929,7 +15929,7 @@ exit:
 static void hdd_driver_unload(void)
 {
 	struct osif_driver_sync *driver_sync;
-	struct hdd_context *hdd_ctx = cds_get_context(QDF_MODULE_ID_HDD);
+	struct hdd_context *hdd_ctx;
 	QDF_STATUS status;
 	void *hif_ctx;
 
@@ -15962,6 +15962,7 @@ static void hdd_driver_unload(void)
 	cds_set_driver_loaded(false);
 	cds_set_unload_in_progress(true);
 
+	hdd_ctx = cds_get_context(QDF_MODULE_ID_HDD);
 	if (hdd_ctx) {
 		hdd_psoc_idle_timer_stop(hdd_ctx);
 		/*