[SCSI] zfcp: fix: avoid race between fc_remote_port_add and scsi_add_device

Flush workqueue of a scsi host after a remote port for that host
is registered at the fc transport class. Otherwise immediate
registration of a scsi device on that host is racy.

Signed-off-by: Andreas Herrmann <aherrman@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>