qcacld-3.0: Check for pdev being NULL

In function ol_txrx_offld_flush, check for pdev being
NULL, before de-referencing it.

Change-Id: I8999d894c74b6ef10cef91345370d859f5eee8ec
CRs-Fixed: 2299780

core/dp/txrx/ol_txrx.c

@@ -4846,6 +4846,11 @@ static void ol_txrx_offld_flush(void *data)
 	if (qdf_unlikely(!sched_ctx))
 		return;
 
+	if (qdf_unlikely(!pdev)) {
+		ol_txrx_err("TXRX module context is NULL");
+		return;
+	}
+
 	if (!ol_cfg_is_rx_thread_enabled(pdev->ctrl_pdev)) {
 		ol_txrx_offld_flush_handler(data, NULL, 0);
 	} else {