init: Don't do grub-mkconfig twice

We need to make grub-mkconfig __after__ the grub-install to allow it
reaching some files like the serial mod.

Commit 8ea72fb60c484a4fab7e7c5a513eef07dcfc63e6, introduced this order
but forgot to remove the first call. Let's keep a single call just after
the install.

I'm fixing the indent too.