ubd_kern: make it 'struct hd_driveid'-free

* Change ubd_id in ubd_ioctl() from 'struct hd_driveid *id'
  to 'u16 *id' and update driver accordingly.

* Include <linux/ata.h> directly instead of through <linux/hdreg.h>.

There should be no functional changes caused by this patch.

Cc: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>