mailmap: Update my email address to @redhat.com

I've brok^D contributed to a few different files in my time at Arm, so
get_maintainer.pl spits out my name from time to time when it's using the
git stats. Make that show an email address that's actually in use.
Signed-off-by: NValentin Schneider <vschneid@redhat.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220406141315.732473-3-vschneid@redhat.com

.mailmap

@@ -391,6 +391,7 @@ Uwe Kleine-König <ukleinek@strlen.de>
 Uwe Kleine-König <ukl@pengutronix.de>
 Uwe Kleine-König <Uwe.Kleine-Koenig@digi.com>
 Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
+Valentin Schneider <vschneid@redhat.com> <valentin.schneider@arm.com>
 Vinod Koul <vkoul@kernel.org> <vinod.koul@intel.com>
 Vinod Koul <vkoul@kernel.org> <vinod.koul@linux.intel.com>
 Vinod Koul <vkoul@kernel.org> <vkoul@infradead.org>