ide: don't tamper with the device register

ide: don't tamper with the device register

In real ISA operation, register writes go out to an entire bus channel
and all listening devices receive the write. The devices do not toggle
the DEV bit based on their own configuration, nor does the HBA
intermediate or tamper with that value.

The reality of the matter is that DEV0/DEV1 accordingly will react to
command register writes based on whether or not the device was selected.

This does not fix a known bug, but it makes the code slightly simpler
and more obvious.

Signed-off-by: John Snow <[email protected]>