dax: advance the iomap_iter on dedupe range

Advance the iter on successful dedupe. Dedupe range uses two iters
and iterates so long as both have outstanding work, so
correspondingly this needs to advance both on each iteration. Since
dax_range_compare_iter() now returns status instead of a byte count,
update the variable name in the caller as well.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Link: https://lore.kernel.org/r/20250224144757.237706-9-bfoster@redhat.com


Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>