staging: comedi: drivers: usbdux.c: fix DMA buffers on stack

fix for instances of DMA buffer on stack(being passed to usb_control_msg) for
the USB-DUX-D Board driver.
Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbdux.c

@@ -730,10 +730,14 @@ static void usbduxsub_ao_IsocIrq(struct urb *urb)
 static int usbduxsub_start(struct usbduxsub *usbduxsub)
 {
 	int errcode = 0;
-	uint8_t local_transfer_buffer[16];
+	uint8_t *local_transfer_buffer;
+
+	local_transfer_buffer = kmalloc(1, GFP_KERNEL);
+	if (!local_transfer_buffer)
+		return -ENOMEM;
 
 	/* 7f92 to zero */
-	local_transfer_buffer[0] = 0;
+	*local_transfer_buffer = 0;
 	errcode = usb_control_msg(usbduxsub->usbdev,
 				  /* create a pipe for a control transfer */
 				  usb_sndctrlpipe(usbduxsub->usbdev, 0),
@@ -751,22 +755,25 @@ static int usbduxsub_start(struct usbduxsub *usbduxsub)
 				  1,
 				  /* Timeout */
 				  BULK_TIMEOUT);
-	if (errcode < 0) {
+	if (errcode < 0)
 		dev_err(&usbduxsub->interface->dev,
 			"comedi_: control msg failed (start)\n");
+
+	kfree(local_transfer_buffer);
 	return errcode;
-	}
-	return 0;
 }
 
 static int usbduxsub_stop(struct usbduxsub *usbduxsub)
 {
 	int errcode = 0;
+	uint8_t *local_transfer_buffer;
 
-	uint8_t local_transfer_buffer[16];
+	local_transfer_buffer = kmalloc(1, GFP_KERNEL);
+	if (!local_transfer_buffer)
+		return -ENOMEM;
 
 	/* 7f92 to one */
-	local_transfer_buffer[0] = 1;
+	*local_transfer_buffer = 1;
 	errcode = usb_control_msg(usbduxsub->usbdev,
 				  usb_sndctrlpipe(usbduxsub->usbdev, 0),
 				  /* bRequest, "Firmware" */
@@ -781,12 +788,12 @@ static int usbduxsub_stop(struct usbduxsub *usbduxsub)
 				  1,
 				  /* Timeout */
 				  BULK_TIMEOUT);
-	if (errcode < 0) {
+	if (errcode < 0)
 		dev_err(&usbduxsub->interface->dev,
 			"comedi_: control msg failed (stop)\n");
+
+	kfree(local_transfer_buffer);
 	return errcode;
-	}
-	return 0;
 }
 
 static int usbduxsub_upload(struct usbduxsub *usbduxsub,