Add guards for mbedtls_psa_crypto_free()

Signed-off-by: Przemek Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/programs/pkey/pk_verify.c b/programs/pkey/pk_verify.c
index 49b5204..96a5d28 100644
--- a/programs/pkey/pk_verify.c
+++ b/programs/pkey/pk_verify.c
@@ -126,7 +126,9 @@
 
 exit:
     mbedtls_pk_free(&pk);
+#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) {