Revert "btrfs: fix the file offset calculation inside btrfs_decompress_buf2page()"

Revert "btrfs: fix the file offset calculation inside btrfs_decompress_buf2page()"

It seems that af566bdaff54 was tested against a tree which did not
contain commit 12851bd921d4 ("fs: Turn page_offset() into a wrapper
around folio_pos()).  Unfortunately it has a bug of its own; on 32-bit
systems, shifting by PAGE_SHIFT will overflow on files larger than 4GiB.
Since page_offset() is now fixed, just revert af566bdaff54.

Fixes: af566bdaff54 (btrfs: fix the file offset calculation inside btrfs_decompress_buf2page())
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Boris Burkov <boris@bur.io>
Tested-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>