Use correct test case conditionals for helper functions in tests/suites

Fix unused-function errors.

Signed-off-by: Michael Schuster <michael@schuster.ms>
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index 0cff121..f197d04 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -467,7 +467,7 @@
 }
 #endif /* MBEDTLS_PSA_CRYPTO_C */
 
-#if defined(MBEDTLS_RSA_C)
+#if defined(MBEDTLS_RSA_C) && defined(MBEDTLS_PK_RSA_ALT_SUPPORT)
 static int mbedtls_rsa_decrypt_func(void *ctx, size_t *olen,
                                     const unsigned char *input, unsigned char *output,
                                     size_t output_max_len)
@@ -491,7 +491,7 @@
 {
     return ((const mbedtls_rsa_context *) ctx)->len;
 }
-#endif /* MBEDTLS_RSA_C */
+#endif /* MBEDTLS_RSA_C && MBEDTLS_PK_RSA_ALT_SUPPORT */
 
 typedef enum {
     /* The values are compatible with thinking of "from pair" as a boolean. */