iommufd: Report unmapped bytes in the error path of iopt_unmap_iova_range

iommufd: Report unmapped bytes in the error path of iopt_unmap_iova_range

There are callers that read the unmapped bytes even when rc != 0. Thus, do
not forget to report it in the error path too.

Fixes: 8d40205f6093 ("iommufd: Add kAPI toward external drivers for kernel access")
Link: https://patch.msgid.link/r/e2b61303bbc008ba1a4e2d7c2a2894749b59fdac.1752126748.git.nicolinc@nvidia.com
Cc: stable@vger.kernel.org
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>