drivers/video: fix build error on CONFIG_DEBUG_OPTLEVEL="-O3"

Summary
The following compilation error occurs after configuring CONFIG_DEBUG_OPTLEVEL="-O3"
CC:  ping.c video/video.c: In function 'video_ioctl':
video/video.c:2347:22: error: 'control.size' may be used uninitialized [-Werror=maybe-uninitialized]
 2347 |               control->size,
      |                      ^~
video/video.c:2273:28: note: 'control' declared here
 2273 |   struct v4l2_ext_control  control;
      |                            ^~~~~~~

Signed-off-by: wangming9 <wangming9@xiaomi.com>

drivers/video/video.c

@@ -2276,6 +2276,9 @@ static int video_g_ctrl(FAR struct video_mng_s *priv,
   struct v4l2_ext_control  control;
   int                      ret;
 
+  memset(&ext_controls, 0, sizeof(struct v4l2_ext_controls));
+  memset(&control, 0, sizeof(struct v4l2_ext_control));
+
   if (ctrl == NULL)
     {
       return -EINVAL;