mm/page_io: rename swap_iocb fields for clarity

mm/page_io: rename swap_iocb fields for clarity

swap_iocb->pages tracks the number of bvec entries (folios), not base
pages.  Rename the array from bvec to bvecs and the counter from pages to
nr_bvecs to accurately reflect their purpose.

Link: https://lore.kernel.org/20260402072650.48811-1-devnexen@gmail.com
Signed-off-by: David Carlier <devnexen@gmail.com>
Suggested-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Acked-by: Chris Li <chrisl@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Kairui Song <kasong@tencent.com>
Cc: Kemeng Shi <shikemeng@huaweicloud.com>
Cc: NeilBrown <neil@brown.name>
Cc: Nhat Pham <nphamcs@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>