media: uvcvideo: Override default flags

When the UVC device has a control that is readonly it doesn't set the
SET_CUR flag. For example the privacy control has SET_CUR flag set in
the defaults in the `uvc_ctrls` variable. Even if the device does not
have it set, it's not cleared by uvc_ctrl_get_flags().

Originally written with assignment in commit 859086ae ("media:
uvcvideo: Apply flags from device to actual properties"). But changed to
|= in commit 0dc68cab ("media: uvcvideo: Prevent setting unavailable
flags"). It would not clear the default flags.

With this patch applied the correct flags are reported to user space.
Tested with:

```
> v4l2-ctl --list-ctrls | grep privacy
privacy 0x009a0910 (bool)   : default=0 value=0 flags=read-only
```
Signed-off-by: Daniel Schaefer <dhs@frame.work>
Fixes: 0dc68cab ("media: uvcvideo: Prevent setting unavailable flags")
Reviewed-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Link: https://lore.kernel.org/r/20240602065053.36850-1-dhs@frame.workSigned-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/media/usb/uvc/uvc_ctrl.c

@@ -2031,7 +2031,13 @@ static int uvc_ctrl_get_flags(struct uvc_device *dev,
 	else
 		ret = uvc_query_ctrl(dev, UVC_GET_INFO, ctrl->entity->id,
 				     dev->intfnum, info->selector, data, 1);
-	if (!ret)
+
+	if (!ret) {
+		info->flags &= ~(UVC_CTRL_FLAG_GET_CUR |
+				 UVC_CTRL_FLAG_SET_CUR |
+				 UVC_CTRL_FLAG_AUTO_UPDATE |
+				 UVC_CTRL_FLAG_ASYNCHRONOUS);
+
 		info->flags |= (data[0] & UVC_CONTROL_CAP_GET ?
 				UVC_CTRL_FLAG_GET_CUR : 0)
 			    |  (data[0] & UVC_CONTROL_CAP_SET ?
@@ -2040,6 +2046,7 @@ static int uvc_ctrl_get_flags(struct uvc_device *dev,
 				UVC_CTRL_FLAG_AUTO_UPDATE : 0)
 			    |  (data[0] & UVC_CONTROL_CAP_ASYNCHRONOUS ?
 				UVC_CTRL_FLAG_ASYNCHRONOUS : 0);
+	}
 
 	kfree(data);
 	return ret;