mailmap: add entry for John Keeping

Map my corporate address to my personal one, as I am leaving the
company.

Link: https://lkml.kernel.org/r/20230531144839.1157112-1-john@keeping.me.uk
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: johnkeeping

.mailmap

@@ -233,6 +233,7 @@ Jisheng Zhang <jszhang@kernel.org> <Jisheng.Zhang@synaptics.com>
 Johan Hovold <johan@kernel.org> <jhovold@gmail.com>
 Johan Hovold <johan@kernel.org> <johan@hovoldconsulting.com>
 John Crispin <john@phrozen.org> <blogic@openwrt.org>
+John Keeping <john@keeping.me.uk> <john@metanate.com>
 John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
 John Stultz <johnstul@us.ibm.com>
 <jon.toppins+linux@gmail.com> <jtoppins@cumulusnetworks.com>