libx265: Fix 'braces around scalar initializer' warning

x265 Reordered the x265_picture fields in the commit

https://github.com/videolan/x265/commit/51b1518de2414431f36eac592db15b667c25a7b9#diff-945b5354d8767dfac13334f2d22cf58fR107

Now the first field is an integer and not an array.

libavcodec/libx265.c

@@ -247,7 +247,7 @@ static int libx265_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
 {
     libx265Context *ctx = avctx->priv_data;
     x265_picture x265pic;
-    x265_picture x265pic_out = { { 0 } };
+    x265_picture x265pic_out = { 0 };
     x265_nal *nal;
     uint8_t *dst;
     int payload = 0;