Remove parentheses of return.

Since return is inconsistent, I removed unnecessary parentheses and
unified them.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4541)
diff --git a/crypto/evp/p_lib.c b/crypto/evp/p_lib.c
index f0c3075..6177e04 100644
--- a/crypto/evp/p_lib.c
+++ b/crypto/evp/p_lib.c
@@ -56,7 +56,7 @@
 
         if (mode >= 0)
             pkey->save_parameters = mode;
-        return (ret);
+        return ret;
     }
 #endif
 #ifndef OPENSSL_NO_EC
@@ -65,10 +65,10 @@
 
         if (mode >= 0)
             pkey->save_parameters = mode;
-        return (ret);
+        return ret;
     }
 #endif
-    return (0);
+    return 0;
 }
 
 int EVP_PKEY_copy_parameters(EVP_PKEY *to, const EVP_PKEY *from)