zonefs: Fix error message in zonefs_file_dio_append()

Since the expected write location in a sequential file is always at the
end of the file (append write), when an invalid write append location is
detected in zonefs_file_dio_append(), print the invalid written location
instead of the expected write location.

Fixes: a608da3b ("zonefs: Detect append writes at invalid locations")
Cc: stable@vger.kernel.org
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>