The variable is called 'have_afalg' and not 'hava_afalg'.

Fixes: f0d92b56 ('introduce some common functions for af_alg backend')
Message-Id: <20200203160046.23194-1-thuth@redhat.com>
Reviewed-by: NDaniel P. Berrangé <berrange@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NLongpeng(Mike) <longpeng2@huawei.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>