util/mkerr.pl: revert accidental change of header guards

This change was backported accidentally from master in commit fbbfd128.
Reviewed-by: NPaul Dale <paul.dale@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/10623)

util/mkerr.pl

@@ -450,8 +450,8 @@ foreach my $lib ( keys %errorfile ) {
  * https://www.openssl.org/source/license.html
  */
 
-#ifndef OPENSSL_${lib}ERR_H
-# define OPENSSL_${lib}ERR_H
+#ifndef HEADER_${lib}ERR_H
+# define HEADER_${lib}ERR_H
 
 # include <openssl/symhacks.h>