CTL: READ(6) should be allowed on CD devices

DOS ASPI drivers use this, with this change applied it is possible to
load a DOS ASPI CDROM driver and run the Windows 98 installer.

Signed-off-by: HP van Braam <hp@tmm.cx>
Reviewed by: imp
Pull Request: https://github.com/freebsd/freebsd-src/pull/1202