avdevice/xv: Increase array size

av_image_copy() expects an array of four pointers according to its
declaration; although it currently only touches pointers that
are actually in use (depending upon the pixel format) this might
change at any time (as has already happened for the linesizes
in d7bc52bf45).

This fixes ticket #9264 as well as a warning from GCC 11.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavdevice/xv.c

@@ -296,7 +296,7 @@ static int write_picture(AVFormatContext *s, uint8_t *input_data[4],
 {
     XVContext *xv = s->priv_data;
     XvImage *img = xv->yuv_image;
-    uint8_t *data[3] = {
+    uint8_t *data[4] = {
         img->data + img->offsets[0],
         img->data + img->offsets[1],
         img->data + img->offsets[2]