Checking in critical places if the mbedtls_platform_zeroize() was successful

Signed-off-by: Piotr Nowicki <piotr.nowicki@arm.com>
diff --git a/tinycrypt/ecc_dh.c b/tinycrypt/ecc_dh.c
index 5a7a9e5..512686c 100644
--- a/tinycrypt/ecc_dh.c
+++ b/tinycrypt/ecc_dh.c
@@ -186,7 +186,9 @@
 	uECC_vli_nativeToBytes(secret, num_bytes, _public);
 
 	/* erasing temporary buffer used to store secret: */
-	mbedtls_platform_zeroize(_private, sizeof(_private));
+	if (_private == mbedtls_platform_zeroize(_private, sizeof(_private))) {
+		return r;
+	}
 
-	return r;
+	return UECC_FAULT_DETECTED;
 }