mailmap: add an entry for Nicolas Schier

Add mapping to linux.dev address as mail usage at work is limited and my
mail provider for private mails is suffering from its own domain name
block lists.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Nicolas Schier <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

.mailmap

···
 Nicolas Pitre <[e-mail]> <[e-mail]>
 Nicolas Saenz Julienne <[e-mail]> <[e-mail]>
 Nicolas Saenz Julienne <[e-mail]> <[e-mail]>
+Nicolas Schier <[e-mail]> <[e-mail]>
+Nicolas Schier <[e-mail]> <[e-mail]>
 Niklas Söderlund <[e-mail]>
 Nikolay Aleksandrov <[e-mail]> <[e-mail]>
 Nikolay Aleksandrov <[e-mail]> <[e-mail]>