orangefs: Pass mapping to orangefs_writepages_work()

orangefs: Pass mapping to orangefs_writepages_work()

Remove two accesses to page->mapping by passing the mapping from
orangefs_writepages() to orangefs_writepages_callback() and then
orangefs_writepages_work().  That makes it obvious that all folios come
from the same mapping, so we can hoist the call to mapping_set_error()
outside the loop.  While I'm here, switch from write_cache_pages()
to writeback_iter() which removes an indirect function call.

Signed-off-by: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Link: https://lore.kernel.org/r/20250305204734.1475264-7-willy@infradead.org
Tested-by: Mike Marshall <hubcap@omnibond.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>