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

This patch fixes an instance of DMA buffer on stack(being passed to
usb_control_msg)for the USB-DUXsigma Board driver. Found using smatch.
Signed-off-by: Kumar Amit Mehta <gmate.amit@gmail.com>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/usbduxsigma.c

@@ -681,7 +681,11 @@ 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(16, GFP_KERNEL);
+	if (!local_transfer_buffer)
+		return -ENOMEM;
 
 	/* 7f92 to zero */
 	local_transfer_buffer[0] = 0;
@@ -702,19 +706,22 @@ 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");
-		return errcode;
-	}
-	return 0;
+
+	kfree(local_transfer_buffer);
+	return errcode;
 }
 
 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(16, GFP_KERNEL);
+	if (!local_transfer_buffer)
+		return -ENOMEM;
 
 	/* 7f92 to one */
 	local_transfer_buffer[0] = 1;
@@ -732,12 +739,12 @@ 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");
-		return errcode;
-	}
-	return 0;
+
+	kfree(local_transfer_buffer);
+	return errcode;
 }
 
 static int usbduxsub_upload(struct usbduxsub *usbduxsub,