MAINTAINERS: update Nick's contact info

Updated .mailmap, but forgot these other places.

Link: https://lkml.kernel.org/r/20250212173523.3979840-1-ndesaulniers@google.com


Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>