ide: Turn debug messages into assertions

These printfs aren't really debug messages, but clearly indicate a bug if they
ever become effective. Noone uses DEBUG_IDE, let's re-enable the check
unconditionally and make it an assertion instead of printfs in the device
emulation.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
