If we're punching a hole in a large folio, we need to remove the
per-folio iomap data as the folio is about to be split and each page will
need its own.  If a dirty folio is only partially-uptodate, the iomap
data contains the information about which blocks cannot be written back,
so assert that a dirty folio is fully uptodate.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>