xfs: zeroing space needs to punch delalloc blocks

When we are zeroing space andit is covered by a delalloc range, we
need to punch the delalloc range out before we truncate the page
cache. Failing to do so leaves and inconsistency between the page
cache and the extent tree, which we later trip over when doing
direct IO over the same range.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Tested-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>