.mailmap: Add an entry for Samer El-Haj-Mahmoud

.mailmap: Add an entry for Samer El-Haj-Mahmoud

We use .mailmap to display contributors email addresses in an
uniform format.

Add an entry for Samer El-Haj-Mahmoud to have his/her name and
email address displayed properly in the git history.

Cc: Samer El-Haj-Mahmoud <elhaj@hpe.com>
Cc: Samer El-Haj-Mahmoud  <samer@elhajmahmoud.com>
Reviewed-by: Samer El-Haj-Mahmoud  <samer@elhajmahmoud.com>
Signed-off-by: Philippe Mathieu-Daude <philmd@redhat.com>
Message-Id: <20200106115415.11624-27-philmd@redhat.com>