mailmap: add entries for Mathieu Othacehe

Add my gnu.org mail address.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Mathieu Othacehe <[e-mail]>
Cc: Bjorn Andersson <[e-mail]>
Cc: Heiko Stuebner <[e-mail]>
Cc: Jakub Kicinski <[e-mail]>
Cc: Jiri Kosina <[e-mail]>
Cc: Konrad Dybcio <[e-mail]>
Cc: Matthieu Baerts <[e-mail]>
Cc: Matt Ranostay <[e-mail]>
Cc: Oleksij Rempel <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

.mailmap

···
 Martin Kepplinger <[e-mail]> <[e-mail]>
 Martin Kepplinger <[e-mail]> <[e-mail]>
 Martyna Szapar-Mudlaw <[e-mail]> <[e-mail]>
-Mathieu Othacehe <[e-mail]>
+Mathieu Othacehe <[e-mail]> <[e-mail]>
 Mat Martineau <[e-mail]> <[e-mail]>
 Mat Martineau <[e-mail]> <[e-mail]>
 Matthew Wilcox <[e-mail]> <[e-mail]>