[media] dw2102: get rid of on-stack dma buffer

usb_control_msg initiates (and waits for completion of) a dma transfer using
the supplied buffer. That buffer thus has to be seperately allocated on
the heap.

In lib/dma_debug.c the function check_for_stack even warns about it:
	WARNING: at lib/dma-debug.c:866 check_for_stack

Note: This change is tested to compile only, as I don't have the hardware.
Signed-off-by: NFlorian Mickler <florian@mickler.org>
Cc: Igor M. Liplianin <liplianin@tut.by>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/dvb/dvb-usb/dw2102.c

@@ -121,12 +121,16 @@ static int dw210x_op_rw(struct usb_device *dev, u8 request, u16 value,
 			u16 index, u8 * data, u16 len, int flags)
 {
 	int ret;
-	u8 u8buf[len];
-
+	u8 *u8buf;
 	unsigned int pipe = (flags == DW210X_READ_MSG) ?
 				usb_rcvctrlpipe(dev, 0) : usb_sndctrlpipe(dev, 0);
 	u8 request_type = (flags == DW210X_READ_MSG) ? USB_DIR_IN : USB_DIR_OUT;
 
+	u8buf = kmalloc(len, GFP_KERNEL);
+	if (!u8buf)
+		return -ENOMEM;
+
+
 	if (flags == DW210X_WRITE_MSG)
 		memcpy(u8buf, data, len);
 	ret = usb_control_msg(dev, pipe, request, request_type | USB_TYPE_VENDOR,
@@ -134,6 +138,8 @@ static int dw210x_op_rw(struct usb_device *dev, u8 request, u16 value,
 
 	if (flags == DW210X_READ_MSG)
 		memcpy(data, u8buf, len);
+
+	kfree(u8buf);
 	return ret;
 }