vhost-scsi: fix wrong vhost-scsi firmware path

vhost-scsi: fix wrong vhost-scsi firmware path

vhost-scsi bootindex does't work because Qemu passes
wrong fireware path to seabios.

before:
  /pci@i0cf8/scsi@7channel@0/vhost-scsi@0,0
after applying the patch:
  /pci@i0cf8/scsi@7/channel@0/vhost-scsi@0,0

Reported-by: Subo <subo7@huawei.com>
Signed-off-by: Gonglei <arei.gonglei@huawei.com>
Message-Id: <1440553971-11108-1-git-send-email-arei.gonglei@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>