util/mkerr.pl: fix perl warning

Gets rid of this;

defined(@array) is deprecated at ../util/mkerr.pl line 792.
        (Maybe you should just omit the defined()?)
defined(@array) is deprecated at ../util/mkerr.pl line 800.
        (Maybe you should just omit the defined()?)

Signed-off-by: Geoff Thorpe <geoff@openssl.org>
(cherry picked from commit 647f360e)