libata: zpodd: Fix small read overflow in zpodd_get_mech_type()

Jeffrin reported a KASAN issue:

  BUG: KASAN: global-out-of-bounds in ata_exec_internal_sg+0x50f/0xc70
  Read of size 16 at addr ffffffff91f41f80 by task scsi_eh_1/149
  ...
  The buggy address belongs to the variable:
    cdb.48319+0x0/0x40

Much like commit 18c9a99b

 ("libata: zpodd: small read overflow in
eject_tray()"), this fixes a cdb[] buffer length, this time in
zpodd_get_mech_type():

We read from the cdb[] buffer in ata_exec_internal_sg(). It has to be
ATAPI_CDB_LEN (16) bytes long, but this buffer is only 12 bytes.

Reported-by: Jeffrin Jose T <jeffrin@rajagiritech.edu.in>
Fixes: afe75951 ("libata: identify and init ZPODD devices")
Link: https://lore.kernel.org/lkml/201907181423.E808958@keescook/


Tested-by: Jeffrin Jose T <jeffrin@rajagiritech.edu.in>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>