MAINTAINERS: update nouveau maintainers

Since I will continue to work on Nouveau consistently, also beyond my
former and still ongoing VM_BIND/EXEC work, add myself to the list of
Nouveau maintainers.

Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230926014913.7721-1-dakr@redhat.com