media: pci: tw686x: no need to check 'next'

If 'done' is not NULL, then next can never be NULL, so just drop
the 'next' check.

This fixes this smatch warning:

drivers/media/pci/tw686x/tw686x-audio.c:62 tw686x_audio_irq() warn: can 'next' even be NULL?
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Cc: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/pci/tw686x/tw686x-audio.c

@@ -59,7 +59,7 @@ void tw686x_audio_irq(struct tw686x_dev *dev, unsigned long requests,
 		}
 		spin_unlock_irqrestore(&ac->lock, flags);
 
-		if (!done || !next)
+		if (!done)
 			continue;
 		/*
 		 * Checking for a non-nil dma_desc[pb]->virt buffer is