btrfs: Use less confusing condition for uptodate parameter to btrfs_writepage_endio_f...

btrfs: Use less confusing condition for uptodate parameter to btrfs_writepage_endio_finish_ordered

The uptodate parameter of btrfs_writepage_endio_finish_ordered is used
to signal whether an error has occured while writing the given page.
0 signals an error, which is propagated to callees and 1 signifies
success. In end_compressed_bio_write the ->bi_status is checked and
based on it either BLK_STS_OK (0) or BLK_STS_NOTSUPP (1) are used. While
from functional point of view this is ok it's a for the poor reader of
the code, since the block layer values are conflated with the semantics
of the parameter.

Just use plain 0 or 1. No functional changes.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>