Add guards for mbedtls_psa_crypto_free()

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/programs/pkey/pk_encrypt.c b/programs/pkey/pk_encrypt.c
index f3c3274..5f5a424 100644
--- a/programs/pkey/pk_encrypt.c
+++ b/programs/pkey/pk_encrypt.c
@@ -153,7 +153,9 @@
     mbedtls_pk_free(&pk);
     mbedtls_entropy_free(&entropy);
     mbedtls_ctr_drbg_free(&ctr_drbg);
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
     mbedtls_psa_crypto_free();
+#endif /* MBEDTLS_USE_PSA_CRYPTO */
 
 #if defined(MBEDTLS_ERROR_C)
     if (exit_code != MBEDTLS_EXIT_SUCCESS) {