media: stkwebcam: move stk_camera_read_reg() scratch buffer to struct stk_camera

In stk_camera_read_reg() a single byte buffer is alloc-ed and
freed on every function call.  Since the size is known,
move the buffer to the struct stk_camera where it will be alloc-ed
and freed once.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>

drivers/media/usb/stkwebcam/stk-webcam.c

@@ -150,25 +150,18 @@ int stk_camera_write_reg(struct stk_camera *dev, u16 index, u8 value)
 int stk_camera_read_reg(struct stk_camera *dev, u16 index, u8 *value)
 {
 	struct usb_device *udev = dev->udev;
-	unsigned char *buf;
 	int ret;
 
-	buf = kmalloc(sizeof(u8), GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
 	ret = usb_control_msg(udev, usb_rcvctrlpipe(udev, 0),
 			0x00,
 			USB_DIR_IN | USB_TYPE_VENDOR | USB_RECIP_DEVICE,
 			0x00,
 			index,
-			buf,
+			&dev->read_reg_scratch,
 			sizeof(u8),
 			500);
 	if (ret >= 0)
-		*value = *buf;
-
-	kfree(buf);
+		*value = dev->read_reg_scratch;
 
 	if (ret < 0)
 		return ret;

drivers/media/usb/stkwebcam/stk-webcam.h

@@ -105,6 +105,8 @@ struct stk_camera {
 	struct list_head sio_avail;
 	struct list_head sio_full;
 	unsigned sequence;
+
+	u8 read_reg_scratch;
 };
 
 #define vdev_to_camera(d) container_of(d, struct stk_camera, vdev)