Don't check for good device status before executing the command in
pmac_ide_do_setfeature() (ide_config_drive_speed() doesn't do this).

It is a job of upper layers to guarantee that the device is ready to
accept new command before we get here.

Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>