wlan: Static code analysis error in WDA_BaCheckActivity.

In WDA_BaCheckActivity added NULL check for pMac before
dereferencing it.

Change-Id: Idba6f84c64ff6b96c4abc9d0508d873fdd0bf739
CRs-Fixed: 737732
diff --git a/CORE/WDA/src/wlan_qct_wda.c b/CORE/WDA/src/wlan_qct_wda.c
index c94e546..23238bd 100644
--- a/CORE/WDA/src/wlan_qct_wda.c
+++ b/CORE/WDA/src/wlan_qct_wda.c
@@ -14388,6 +14388,14 @@
       return ;
    }
    pMac = (tpAniSirGlobal )VOS_GET_MAC_CTXT(pWDA->pVosContext);
+   if(NULL == pMac)
+   {
+      VOS_TRACE( VOS_MODULE_ID_WDA, VOS_TRACE_LEVEL_ERROR,
+                          "%s: pMac is NULL",__func__);
+      VOS_ASSERT(0);
+      return ;
+   }
+
    if (wlan_cfgGetInt(pMac,
            WNI_CFG_DEL_ALL_RX_TX_BA_SESSIONS_2_4_G_BTC, &val) !=
                                                       eSIR_SUCCESS)