Add guards for mbedtls_psa_crypto_free()

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/programs/x509/cert_req.c b/programs/x509/cert_req.c
index 43b1eb1..db200d9 100644
--- a/programs/x509/cert_req.c
+++ b/programs/x509/cert_req.c
@@ -374,7 +374,9 @@
     mbedtls_pk_free(&key);
     mbedtls_ctr_drbg_free(&ctr_drbg);
     mbedtls_entropy_free(&entropy);
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
     mbedtls_psa_crypto_free();
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(_WIN32)
     mbedtls_printf("  + Press Enter to exit this program.\n");