atap: Fix missing return statement compile error

Change-Id: Icf7295da1eb1f4e36a6f37f90457105c4432fd77
diff --git a/atap/trusty_atap_ops.cpp b/atap/trusty_atap_ops.cpp
index 4f50879..6b3df13 100644
--- a/atap/trusty_atap_ops.cpp
+++ b/atap/trusty_atap_ops.cpp
@@ -98,6 +98,7 @@
             return ATAP_RESULT_ERROR_STORAGE;
         }
     }
+    return ATAP_RESULT_OK;
 }
 
 AtapResult TrustyAtapOps::read_attestation_public_key(AtapKeyType key_type,