efi/esrt: Don't preformat name

kobject_init_and_add takes a format string+args, so there's no reason
to do this formatting in advance.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Peter Jones <pjones@redhat.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>