staging: comedi: gsc_hpdi: check dma_alloc_coherent() return value

The "auto-attach" handler function `gsc_hpdi_auto_attach()` calls
`dma_alloc_coherent()` in a loop to allocate some DMA data buffers, and
also calls it to allocate a buffer for a DMA descriptor chain.  However,
it does not check the return value of any of these calls.  Change
`gsc_hpdi_auto_attach()` to return `-ENOMEM` if any of these
`dma_alloc_coherent()` calls fail.  This will result in the comedi core
calling the "detach" handler `gsc_hpdi_detach()` as part of the
clean-up, which will call `gsc_hpdi_free_dma()` to free any allocated
DMA coherent memory buffers.

Cc: <stable@vger.kernel.org> #4.6+
Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Link: https://lore.kernel.org/r/20191216110823.216237-1-abbotti@mev.co.ukSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/gsc_hpdi.c

@@ -623,6 +623,11 @@ static int gsc_hpdi_auto_attach(struct comedi_device *dev,
 		    dma_alloc_coherent(&pcidev->dev, DMA_BUFFER_SIZE,
 				       &devpriv->dio_buffer_phys_addr[i],
 				       GFP_KERNEL);
+		if (!devpriv->dio_buffer[i]) {
+			dev_warn(dev->class_dev,
+				 "failed to allocate DMA buffer\n");
+			return -ENOMEM;
+		}
 	}
 	/* allocate dma descriptors */
 	devpriv->dma_desc = dma_alloc_coherent(&pcidev->dev,
@@ -630,6 +635,11 @@ static int gsc_hpdi_auto_attach(struct comedi_device *dev,
 					       NUM_DMA_DESCRIPTORS,
 					       &devpriv->dma_desc_phys_addr,
 					       GFP_KERNEL);
+	if (!devpriv->dma_desc) {
+		dev_warn(dev->class_dev,
+			 "failed to allocate DMA descriptors\n");
+		return -ENOMEM;
+	}
 	if (devpriv->dma_desc_phys_addr & 0xf) {
 		dev_warn(dev->class_dev,
 			 " dma descriptors not quad-word aligned (bug)\n");