iomap: rename iomap_iter processed field to status

iomap: rename iomap_iter processed field to status

The iter.processed field name is no longer appropriate now that
iomap operations do not return the number of bytes processed. Rename
the field to iter.status to reflect that a success or error code is
expected.

Also change the type to int as there is no longer a need for an s64.
This reduces the size of iomap_iter by 8 bytes due to a combination
of smaller type and reduction in structure padding. While here, fix
up the return types of various _iter() helpers to reflect the type
change.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Link: https://lore.kernel.org/r/20250224144757.237706-12-bfoster@redhat.com
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>