CREDITS: update email address for Martin Kepplinger

Employers change - Linux stays. Also, add my (long time valid) GPG key
fingerprint to the contact details.
Signed-off-by: Martin Kepplinger <martin.kepplinger@puri.sm>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

CREDITS

@@ -1871,8 +1871,9 @@ S: The Netherlands
 
 N: Martin Kepplinger
 E: martink@posteo.de
-E: martin.kepplinger@ginzinger.com
+E: martin.kepplinger@puri.sm
 W: http://www.martinkepplinger.com
+P: 4096R/5AB387D3 F208 2B88 0F9E 4239 3468  6E3F 5003 98DF 5AB3 87D3
 D: mma8452 accelerators iio driver
 D: pegasus_notetaker input driver
 D: Kernel fixes and cleanups