mm/mm_init: use helper macro BITS_PER_LONG and BITS_PER_BYTE

It's more readable to use helper macro BITS_PER_LONG and BITS_PER_BYTE. 
No functional change intended.

Link: https://lkml.kernel.org/r/20230807023528.325191-1-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>