ipr: Wait to do async scan until scsi host is initialized

When performing an async scan, make sure the kthread doing scanning
doesn't start before the scsi host is fully initialized.

Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Reviewed-by: Gabriel Krisman Bertazi <krisman@linux.vnet.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>