btrfs: use folio_contains() for EOF detection

Currently we use the following pattern to detect if the folio contains
the end of a file:

	if (folio->index == end_index)
		folio_zero_range();

But that only works if the folio is page sized.

For the following case, it will not work and leave the range beyond EOF
uninitialized:

  The page size is 4K, and the fs block size is also 4K.

	16K        20K       24K
        |          |     |   |
	                 |
                         EOF at 22K

And we have a large folio sized 8K at file offset 16K.

In that case, the old "folio->index == end_index" will not work, thus
the range [22K, 24K) will not be zeroed out.

Fix the following call sites which use the above pattern:

- add_ra_bio_pages()

- extent_writepage()

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

fs/btrfs/compression.c

@@ -523,7 +523,7 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 		free_extent_map(em);
 		unlock_extent(tree, cur, page_end, NULL);
 
-		if (folio->index == end_index) {
+		if (folio_contains(folio, end_index)) {
 			size_t zero_offset = offset_in_folio(folio, isize);
 
 			if (zero_offset) {