mailmap: add new email address for Martin Kepplinger

Include my new email address for tracking my contributions.
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

.mailmap

@@ -151,6 +151,7 @@ Mark Brown <broonie@sirena.org.uk>
 Mark Yao <markyao0591@gmail.com> <mark.yao@rock-chips.com>
 Martin Kepplinger <martink@posteo.de> <martin.kepplinger@theobroma-systems.com>
 Martin Kepplinger <martink@posteo.de> <martin.kepplinger@ginzinger.com>
+Martin Kepplinger <martink@posteo.de> <martin.kepplinger@puri.sm>
 Mathieu Othacehe <m.othacehe@gmail.com>
 Matthew Wilcox <willy@infradead.org> <matthew.r.wilcox@intel.com>
 Matthew Wilcox <willy@infradead.org> <matthew@wil.cx>