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: Valentin Schneider <vschneid@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220406141315.732473-3-vschneid@redhat.com