wlan: Fix possible null pointer dereference in WDA_IsSelfSTA

In function WDA_IsSelfSTA(), pointer pWDA will be NULL
dereferenced if VOS_GET_WDA_CTXT() returns NULL.
Added NULL pointer check before accessing the pointer.

Change-Id: I40dcac790d0bc76939c13b4af864139889403a02
CRs-Fixed: 679406
diff --git a/CORE/WDA/src/wlan_qct_wda.c b/CORE/WDA/src/wlan_qct_wda.c
index 133a654..e61543c 100644
--- a/CORE/WDA/src/wlan_qct_wda.c
+++ b/CORE/WDA/src/wlan_qct_wda.c
@@ -10246,7 +10246,10 @@
 
   tWDA_CbContext *pWDA = (tWDA_CbContext *)VOS_GET_WDA_CTXT(pVosContext);
 
-  return WDI_IsSelfSTA(pWDA->pWdiContext,ucSTAIdx);
+  if (NULL != pWDA)
+     return WDI_IsSelfSTA(pWDA->pWdiContext,ucSTAIdx);
+  else
+     return VOS_TRUE;
 }
 /*
  * FUNCTION: WDA_NvDownloadReqCallback