Report ready DVD status to CDVDMAN

* Early on the IOP continiously reads from 0x1F402005 which
is the N command status register [1], to know if it's
ready or not. So it be safe, let's report that the drive is ready
by returning 0x40 (bit 6 set)

[1] https://psi-rockin.github.io/ps2tek/#cdvdioports