mailmap: add entry for Sean Nyekjaer

As I no longer is working for Prevas, add a mailmap entry
so any mail directed towards me reaches the appropriate mailbox.

Secondly. point to my work mail instead of my private one.

Signed-off-by: Sean Nyekjaer <sean@geanix.com>
diff --git a/.mailmap b/.mailmap
index ea08870..ab9dc5a 100644
--- a/.mailmap
+++ b/.mailmap
@@ -28,3 +28,5 @@
 Xiaorui Hu <xiaorui.hu@linaro.org>
 Yannis Damigos <giannis.damigos@gmail.com> <ydamigos@iccs.gr>
 Vinayak Kariappa Chettimada <vinayak.kariappa.chettimada@nordicsemi.no> <vinayak.kariappa.chettimada@nordicsemi.no> <vich@nordicsemi.no> <vinayak.kariappa@gmail.com>
+Sean Nyekjaer <sean@geanix.com> <sean.nyekjaer@prevas.dk>
+Sean Nyekjaer <sean@geanix.com> <sean@nyekjaer.dk>