[SCSI] fix SCSI_IOCTL_PROBE_HOST

This returns always false with new-style drivers right now.  Make it
return always true instead, as a host must be present if we are able
to call the ioctl (without a host attached there would be no device
node to call on..)

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>