PIO mode is setup by different code, and it takes care of the IORDY 
setting according to the PIO rules (and it gets called). DMA mode setup should 
just ignore the IORDY setting as in all other sane drivers.

Well it can't ignore it - but if you mean just keep the bit as is then
that sounds sensible, have to see what the docs say happens if you ever
set MWDMA without IORDY.