mpage: convert map_buffer_to_folio() to folio_create_empty_buffers()

Saves a folio->page->folio conversion.

Link: https://lkml.kernel.org/r/20231016201114.1928083-4-willy@infradead.org


Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>