btrfs: prepare btrfs_page_mkwrite() for large data folios

btrfs: prepare btrfs_page_mkwrite() for large data folios

The function btrfs_page_mkwrite() has an explicit ASSERT() checking the
folio order.

To make it support large data folios, we need to:

- Remove the ASSERT(folio_order(folio) == 0)

- Use folio_contains() to check if the folio covers the last page

Otherwise the code is already supporting large folios well.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>