mailmap: update email for Iskren Chernev

I'm sunsetting my gmail account and moving to personal domain.

Link: https://lkml.kernel.org/r/20221124114356.2187901-1-me@iskren.info


Signed-off-by: Iskren Chernev <me@iskren.info>
Acked-by: Iskren Chernev <iskren.chernev@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>