ide: use wait_drive_not_busy() in drive_cmd_intr() (take 2)

Use wait_drive_not_busy() in drive_cmd_intr().

v2:
* Fix wait_drive_not_busy() comment (noticed by Sergei).

Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>