lavc/qsvenc: set base address for V plane

The SDK checks Data.V when using system memory for VP9 encoding. This
fixed the error below:

$ ffmpeg -qsv_device /dev/dri/renderD129 -f lavfi -i yuvtestsrc -c:v
vp9_qsv -f null -

[vp9_qsv @ 0x55b8387cbe90] Error during encoding: NULL pointer (-2)
Video encoding failed

Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>

libavcodec/qsvenc.c

@@ -1535,8 +1535,23 @@ static int submit_frame(QSVEncContext *q, const AVFrame *frame,
         qf->surface.Data.PitchLow  = qf->frame->linesize[0];
         qf->surface.Data.Y         = qf->frame->data[0];
         qf->surface.Data.UV        = qf->frame->data[1];
-    }
 
+        /* The SDK checks Data.V when using system memory for VP9 encoding */
+        switch (frame->format) {
+        case AV_PIX_FMT_NV12:
+            qf->surface.Data.V     = qf->surface.Data.UV + 1;
+            break;
+
+        case AV_PIX_FMT_P010:
+            qf->surface.Data.V     = qf->surface.Data.UV + 2;
+            break;
+
+        default:
+            /* should not reach here */
+            av_assert0(0);
+            break;
+        }
+    }
     qf->surface.Data.TimeStamp = av_rescale_q(frame->pts, q->avctx->time_base, (AVRational){1, 90000});
 
     *new_frame = qf;