MAINTAINERS: Update Drew Fustini's email address

Switch from personal domain to kernel.org address.

Signed-off-by: Drew Fustini <fustini@kernel.org>
Link: https://lore.kernel.org/r/20250619035457.331065-1-fustini@kernel.org


Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>