Olaf Hering noticed that SG_IO was no-longer working correctly on some
CD-ROMS.  The reason is a change in behaviour induced by switching to
the new scsi_test_unit_ready() API.

Apparently the CD-ROM special case needs to ignore both UNIT_ATTENTION
and NOT_READY for removable media.
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>