staging: comedi: addi_apci_3120: simplify setting of devpriv->us_UseDma

`apci3120_auto_attach()` first sets `devpriv->us_UseDma` to 1, then sets
it back to 0 if it fails to allocate the DMA buffer.  Since `*devpriv`
is initially zeroed out by `comedi_alloc_devpriv()`, change it to only
set `devpriv->us_UseDma` to 1 if the allocation succeeds.  Also, don't
bother explicitly initializing `devpriv->b_DmaDoubleBuffer` to 0 as it
is already zeroed out.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/addi_apci_3120.c

@@ -88,10 +88,7 @@ static int apci3120_auto_attach(struct comedi_device *dev,
 			dev->irq = pcidev->irq;
 	}
 
-	devpriv->us_UseDma = 1;
-
 	/* Allocate DMA buffers */
-	devpriv->b_DmaDoubleBuffer = 0;
 	for (i = 0; i < 2; i++) {
 		for (order = 2; order >= 0; order--) {
 			devpriv->ul_DmaBufferVirtual[i] =
@@ -106,8 +103,8 @@ static int apci3120_auto_attach(struct comedi_device *dev,
 			break;
 		devpriv->ui_DmaBufferSize[i] = PAGE_SIZE << order;
 	}
-	if (!devpriv->ul_DmaBufferVirtual[0])
-		devpriv->us_UseDma = 0;
+	if (devpriv->ul_DmaBufferVirtual[0])
+		devpriv->us_UseDma = 1;
 
 	if (devpriv->ul_DmaBufferVirtual[1])
 		devpriv->b_DmaDoubleBuffer = 1;