sparc64: remove unnecessary log message

There is no need to log message if ATU hvapi couldn't get register.
Unlike PCI hvapi, ATU hvapi registration failure is not hard error.
Even if ATU hvapi registration fails (on system with ATU or without
ATU) system continues with legacy IOMMU. So only log message when
ATU hvapi successfully get registered.

Signed-off-by: Tushar Dave <tushar.n.dave@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>