[media] touptek: don't DMA at the stack

As warned by smatch:
	drivers/media/usb/gspca/touptek.c:220 reg_w() error: doing dma on the stack (buff)
	drivers/media/usb/gspca/touptek.c:458 configure() error: doing dma on the stack (buff)

This can fail, as the stack may not be in a memory that would
allod DMA. So, use the usb_buf instead.
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/usb/gspca/touptek.c

@@ -211,7 +211,7 @@ static int val_reply(struct gspca_dev *gspca_dev, const char *reply, int rc)
 
 static void reg_w(struct gspca_dev *gspca_dev, u16 value, u16 index)
 {
-	char buff[1];
+	char *buff = gspca_dev->usb_buf;
 	int rc;
 
 	PDEBUG(D_USBO,
@@ -438,7 +438,7 @@ static void configure_encrypted(struct gspca_dev *gspca_dev)
 static int configure(struct gspca_dev *gspca_dev)
 {
 	int rc;
-	uint8_t buff[4];
+	char *buff = gspca_dev->usb_buf;
 
 	PDEBUG(D_STREAM, "configure()\n");