libavfilter/vf_overlay_qsv: Use format of first input to set output format for overlay_qsv

overlay_qsv hard coded to use nv12 as output format. Now use the format
of the first input to set output format.

For detailed information of supported format on different platform,
please see the "composition" rows in "Video Processing Features" at
below link:
https://www.intel.com/content/www/us/en/develop/documentation/media-capabilities-of-intel-hardware/top.html

Signed-off-by: Wenbin Chen <wenbin.chen@intel.com>
Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>

libavfilter/vf_overlay_qsv.c

@@ -276,6 +276,7 @@ static int config_output(AVFilterLink *outlink)
     int ret;
 
     av_log(ctx, AV_LOG_DEBUG, "Output is of %s.\n", av_get_pix_fmt_name(outlink->format));
+    vpp->qsv_param.out_sw_format = in0->format;
     if ((in0->format == AV_PIX_FMT_QSV && in1->format != AV_PIX_FMT_QSV) ||
         (in0->format != AV_PIX_FMT_QSV && in1->format == AV_PIX_FMT_QSV)) {
         av_log(ctx, AV_LOG_ERROR, "Mixing hardware and software pixel formats is not supported.\n");
@@ -288,6 +289,7 @@ static int config_output(AVFilterLink *outlink)
             av_log(ctx, AV_LOG_ERROR, "Inputs with different underlying QSV devices are forbidden.\n");
             return AVERROR(EINVAL);
         }
+        vpp->qsv_param.out_sw_format = hw_frame0->sw_format;
     }
 
     outlink->w          = vpp->var_values[VAR_MW];