Fix ret code in ecdh_curve25519.c
diff --git a/programs/pkey/ecdh_curve25519.c b/programs/pkey/ecdh_curve25519.c
index e7ead9a..1f52126 100644
--- a/programs/pkey/ecdh_curve25519.c
+++ b/programs/pkey/ecdh_curve25519.c
@@ -29,8 +29,11 @@
 #include "mbedtls/platform.h"
 #else
 #include <stdio.h>
-#define mbedtls_printf     printf
-#endif
+#include <stdlib.h>
+#define mbedtls_printf          printf
+#define MBEDTLS_EXTI_SUCCESS    EXIT_SUCCESS
+#define MBEDTLS_EXIT_FAILURE    EXIT_FAILURE
+#endif /* MBEDTLS_PLATFORM_C */
 
 #if !defined(MBEDTLS_ECDH_C) || \
     !defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED) || \
@@ -51,7 +54,8 @@
 
 int main( int argc, char *argv[] )
 {
-    int ret;
+    int ret = 1;
+    int exit_code = MBEDTLS_EXIT_FAILURE;
     mbedtls_ecdh_context ctx_cli, ctx_srv;
     mbedtls_entropy_context entropy;
     mbedtls_ctr_drbg_context ctr_drbg;
@@ -218,6 +222,7 @@
 
     mbedtls_printf( " ok\n" );
 
+    exit_code = MBEDTLS_EXIT_SUCCESS;
 
 exit:
 
@@ -231,7 +236,7 @@
     mbedtls_ctr_drbg_free( &ctr_drbg );
     mbedtls_entropy_free( &entropy );
 
-    return( ret != 0 );
+    return( exit_code );
 }
 #endif /* MBEDTLS_ECDH_C && MBEDTLS_ECP_DP_CURVE25519_ENABLED &&
           MBEDTLS_ENTROPY_C && MBEDTLS_CTR_DRBG_C */