mm/sparse-vmemmap.c: remove unwanted initialization in vmemmap_populate_compound_pages()

mm/sparse-vmemmap.c: remove unwanted initialization in vmemmap_populate_compound_pages()

Remove unnecessary initialization for the variable 'next'.  This fixes
the clang scan warning: Value stored to 'next' during its
initialization is never read [deadcode.DeadStores]

Link: https://lkml.kernel.org/r/20220612182320.160651-1-gautammenghani201@gmail.com
Signed-off-by: Gautam Menghani <gautammenghani201@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>