Removes p_rng param from mbedtls_rsa_rsassa_pss_verify_ext

Commit removes p_rng parameter from the
mbedtls_rsa_rsassa_pss_verify_ext function
in preparation for removal of the mode
parameter.

Signed-off-by: Thomas Daubney <thomas.daubney@arm.com>
diff --git a/tests/suites/test_suite_pkcs1_v21.function b/tests/suites/test_suite_pkcs1_v21.function
index 0983a42..82f33d6 100644
--- a/tests/suites/test_suite_pkcs1_v21.function
+++ b/tests/suites/test_suite_pkcs1_v21.function
@@ -248,7 +248,7 @@
                                            hash_len, hash_result,
                                            result_str->x ) == result_simple );
 
-    TEST_ASSERT( mbedtls_rsa_rsassa_pss_verify_ext( &ctx, NULL, NULL, MBEDTLS_RSA_PUBLIC,
+    TEST_ASSERT( mbedtls_rsa_rsassa_pss_verify_ext( &ctx, NULL, MBEDTLS_RSA_PUBLIC,
                                         msg_digest_id, hash_len, hash_result,
                                         mgf_hash, salt_len,
                                         result_str->x ) == result_full );