Rename ATTACK_DETECTED to FAULT_DETECTED

We don't know for sure it's an attack, it could be the hardware failing
randomly as well.
diff --git a/library/pk.c b/library/pk.c
index 05ffe1c..fbe711d 100644
--- a/library/pk.c
+++ b/library/pk.c
@@ -592,7 +592,7 @@
     ret_fi = uECC_verify( keypair->public_key, hash,
                           (unsigned) hash_len, signature );
 
-    if( ret_fi == UECC_ATTACK_DETECTED )
+    if( ret_fi == UECC_FAULT_DETECTED )
         return( MBEDTLS_ERR_PLATFORM_FAULT_DETECTED );
 
     if( ret_fi == UECC_SUCCESS )