dpt_i2o fixes for stable

I'm proposing to address the most obvious issues with dpt_i2o on stable branches. At this stage it may be better to remove it as has been done upstream, but I'd rather limit the regression for anyone still using the hardware.

The changes are:

- "scsi: dpt_i2o: Remove broken pass-through ioctl (I2OUSERCMD)", which closes security flaws including CVE-2023-2007. - "scsi: dpt_i2o: Do not process completions with invalid addresses", which removes the remaining bus_to_virt() call and may slightly improve handling of misbehaving hardware.

These changes have been compiled on all the relevant stable branches, but I don't have hardware to test on.

Ben.