qcacld-3.0: Set lim_join_req to NULL once it's freed

Currently, pe_session->lim_join_req is freed when there is a
failure in creation/filling the session for link. The same is
attempted to free in pe_delete_session() also.
Set it to NULL once it's freed to avoid double-free.

Change-Id: I6908fc768d782dfe4fe542ccb75ba2cabeb52d0f
CRs-Fixed: 3310292

core/mac/src/pe/lim/lim_api.c

@@ -3307,8 +3307,10 @@ lim_cm_fill_link_session(struct mac_context *mac_ctx,
 		pe_session->limMlmState = eLIM_MLM_WT_REASSOC_RSP_STATE;
 	}
 end:
-	if (QDF_IS_STATUS_ERROR(status))
+	if (QDF_IS_STATUS_ERROR(status)) {
 		qdf_mem_free(pe_session->lim_join_req);
+		pe_session->lim_join_req = NULL;
+	}
 	return status;
 }