xfs: Propagate errors from xfs_reflink_cancel_cow_range in xfs_dax_write_iomap_end

In xfs_dax_write_iomap_end(), directly return the result of
xfs_reflink_cancel_cow_range() when !written, ensuring proper
error propagation and improving code robustness.

Fixes: ea6c49b7 ("xfs: support CoW in fsdax mode")
Cc: stable@vger.kernel.org # v6.0
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Wentao Liang <vulab@iscas.ac.cn>
Signed-off-by: Carlos Maiolino <cem@kernel.org>