pktcdvd: Use DEFINE_SHOW_ATTRIBUTE() to simplify code

Use DEFINE_SHOW_ATTRIBUTE() helper macro to simplify the code.
No functional change.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/20230310164549.22133-7-andriy.shevchenko@linux.intel.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>