Fix incorrect function name

There is no such function as `EVP_EVP_aes_128_cbc()` in openssl.
This should read `EVP_aes_128_cbc()`

In order to see a compilation failure due to this, it is necessary to
build a version of openssl without any of the older and less secure
ciphers, including omitting DES/3DES.

Previously submitted as ruby/ruby#11515 --
resubmitting here as requested.

ext/openssl/ossl_pkcs7.c

@@ -281,7 +281,7 @@ ossl_pkcs7_s_encrypt(int argc, VALUE *argv, VALUE klass)
 #elif !defined(OPENSSL_NO_RC2)
 	ciph = EVP_rc2_40_cbc();
 #elif !defined(OPENSSL_NO_AES)
-	ciph = EVP_EVP_aes_128_cbc();
+	ciph = EVP_aes_128_cbc();
 #else
 	ossl_raise(ePKCS7Error, "Must specify cipher");
 #endif