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>
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