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/tinycrypt/ecc_dsa.c b/tinycrypt/ecc_dsa.c
index 87fa53b..0d6683b 100644
--- a/tinycrypt/ecc_dsa.c
+++ b/tinycrypt/ecc_dsa.c
@@ -304,7 +304,7 @@
 			return UECC_SUCCESS;
 		}
 		else {
-			return UECC_ATTACK_DETECTED;
+			return UECC_FAULT_DETECTED;
 		}
 	}