iommu: Move lock from iommu_change_dev_def_domain() to its caller

The intention is to make it possible to put group ownership check and
default domain change in a same critical region protected by the group's
mutex lock. No intentional functional change.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230322064956.263419-5-baolu.lu@linux.intel.com


Signed-off-by: Joerg Roedel <jroedel@suse.de>