mm, swap: rename helper for setup bad slots

mm, swap: rename helper for setup bad slots

The name inc_cluster_info_page is very confusing, as this helper is only
used during swapon to mark bad slots.  Rename it properly and turn the
VM_BUG_ON in it into WARN_ON to expose more potential issues.  Swapon is a
cold path, so adding more checks should be a good idea.

No feature change except new WARN_ON.

Link: https://lkml.kernel.org/r/20251024-swap-clean-after-swap-table-p1-v2-2-a709469052e7@tencent.com
Signed-off-by: Kairui Song <kasong@tencent.com>
Acked-by: Chris Li <chrisl@kernel.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Barry Song <baohua@kernel.org>
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>