cdrom: handle TOC

This patch should fix TOC handling for cdroms that can not play audio.  It
extends commit af744e32

 ("cdrom: don't
check CDC_PLAY_AUDIO in cdrom_count_tracks()") with a safety check and
non-audio ioctls support.

Since CDC_PLAY_AUDIO flag was used not only to check ability to play audio
but also to ensure that audio_ioctl was not NULL, all TOC-related
operations had to use it.

As far as I understand, now audio_ioctl is never NULL, so a sanity check
during device registration should be sufficient.

It was tested on Optiarc AD7203A device, that has no ability to play
audio.

Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <jens.axboe@oracle.com>
Cc: Borislav Petkov <petkovbb@googlemail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[bart: remove now unneeded ->audio_ioctl check (noticed by Borislav)]
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>