qcacld-3.0: Handle NULL pdev in cds_flush_cache_rx_queue()

Currently cds_flush_cache_rx_queue() does not verify that
cds_get_context() returns a valid pdev which could subsequently lead
to dereferencing an invalid pointer.  Add a validity check for this
pointer.

Change-Id: I326e0b92205fda78854c947248e675d287a7ec04
CRs-Fixed: 1082035
(cherry picked from commit 514e12df3c66ef0e457d76ef8c984874481f5117)

core/cds/src/cds_api.c

@@ -836,7 +836,11 @@ void cds_flush_cache_rx_queue(void)
 {
 	uint8_t sta_id;
 	struct ol_txrx_peer_t *peer;
-	struct ol_txrx_pdev_t *pdev = cds_get_context(QDF_MODULE_ID_TXRX);
+	struct ol_txrx_pdev_t *pdev;
+
+	pdev = cds_get_context(QDF_MODULE_ID_TXRX);
+	if (!pdev)
+		return;
 
 	for (sta_id = 0; sta_id < WLAN_MAX_STA_COUNT; sta_id++) {
 		peer = ol_txrx_peer_find_by_local_id(pdev, sta_id);