libata: Fix compile warning with ATA_DEBUG enabled

This fixs the following comile warnings with ATA_DEBUG enabled,
which detected by Linaro GCC 5.2-2015.11:

  drivers/ata/libata-scsi.c: In function 'ata_scsi_dump_cdb':
  ./include/linux/kern_levels.h:5:18: warning: format '%d' expects
  argument of type 'int', but argument 6 has type 'u64 {aka long
   long unsigned int}' [-Wformat=]

tj: Patch hand-applied and description trimmed.

Signed-off-by: Dong Bo <dongbo4@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>