mm/mm_init.c: move nr_initialised reset down a bit

mm/mm_init.c: move nr_initialised reset down a bit

We don't need to count nr_initialised in two cases:

* for low zones that are always populated
* after first_deferred_pfn is detected

Let's move the nr_initialised reset down a bit to reduce some comparison
of prev_end_pfn and end_pfn.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Link: https://lore.kernel.org/r/20240525023040.13509-3-richard.weiyang@gmail.com
Signed-off-by: Mike Rapoport (IBM) <rppt@kernel.org>