Consistent formatting for sizeof(foo)

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4872)
diff --git a/apps/errstr.c b/apps/errstr.c
index 324e6e4..3ce4acf 100644
--- a/apps/errstr.c
+++ b/apps/errstr.c
@@ -57,7 +57,7 @@
              */
             OPENSSL_init_ssl(OPENSSL_INIT_LOAD_SSL_STRINGS
                              | OPENSSL_INIT_LOAD_CRYPTO_STRINGS, NULL);
-            ERR_error_string_n(l, buf, sizeof buf);
+            ERR_error_string_n(l, buf, sizeof(buf));
             BIO_printf(bio_out, "%s\n", buf);
         }
     }