btrfs: subpage: make compress_file_range() compatible

In function compress_file_range(), when the compression is finished, the
function just rounds up @total_in to PAGE_SIZE.  This is fine for
regular sectorsize == PAGE_SIZE case, but not for subpage.

Just change the ALIGN(, PAGE_SIZE) to round_up(, sectorsize) so that
both regular sectorsize and subpage sectorsize will be happy.

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