Modify PK test suite to provide PRNG to RSA signature function

To prepare for the option of mandatory blinding, this commit changes
the PK test suite to always call signature functions with a PRNG.
diff --git a/tests/suites/test_suite_pk.function b/tests/suites/test_suite_pk.function
index 5fa8a69..33453ac 100644
--- a/tests/suites/test_suite_pk.function
+++ b/tests/suites/test_suite_pk.function
@@ -43,7 +43,7 @@
                        const unsigned char *input, unsigned char *output,
                        size_t output_max_len )
 {
-    return( mbedtls_rsa_pkcs1_decrypt( (mbedtls_rsa_context *) ctx, NULL, NULL, mode, olen,
+    return( mbedtls_rsa_pkcs1_decrypt( (mbedtls_rsa_context *) ctx, rnd_std_rand, NULL, mode, olen,
                                input, output, output_max_len ) );
 }
 int mbedtls_rsa_sign_func( void *ctx,
@@ -51,7 +51,9 @@
                    int mode, mbedtls_md_type_t md_alg, unsigned int hashlen,
                    const unsigned char *hash, unsigned char *sig )
 {
-    return( mbedtls_rsa_pkcs1_sign( (mbedtls_rsa_context *) ctx, f_rng, p_rng, mode,
+    ((void) f_rng);
+    ((void) p_rng);
+    return( mbedtls_rsa_pkcs1_sign( (mbedtls_rsa_context *) ctx, rnd_std_rand, NULL, mode,
                             md_alg, hashlen, hash, sig ) );
 }
 size_t mbedtls_rsa_key_len_func( void *ctx )