lavfi/vf_vpp_qsv: fix the time_base for outlink

Since commit 89ffcd1, the status pts of the output link is set to a
value in the input link time base, not in the output link time base when
EOF is reached. Usually this pst value is larger than the required one
because the output link time base is more greater than the input link
time base. When "-vf vpp_qsv,fps" is used, user has to wait a long time
for the ending of the pipeline because fps filter output a huge number
of frames until the wrong status pts is hit.

The issue can be triggered with the command below (use a clip with 1000
frames in this case):

$> time ffmpeg -hwaccel qsv -c:v hevc_qsv -i input.h265 -vf
"vpp_qsv=w=1920:h=1080,fps=fps=30" -f null -
...
[out_0_0 @ 0x564ccd27e020] 10000000 buffers queued in out_0_0, something
may be wrong.
frame=40119596 fps=88080 q=-0.0 Lsize=N/A time=371:28:39.96 bitrate=N/A
speed=2.94e+03x
video:17238889kB audio:0kB subtitle:0kB other streams:0kB global
headers:0kB muxing overhead: unknown

real    9m7.451s
user    2m34.102s
sys     0m39.734s

In order to avoid the above issue, the same time base for input and
ouput links is used in this patch.

Fixes ticket #9286

Signed-off-by: Zhong Li <zhongli_dev@126.com>

libavfilter/vf_vpp_qsv.c

@@ -303,7 +303,7 @@ static int config_output(AVFilterLink *outlink)
     outlink->w          = vpp->out_width;
     outlink->h          = vpp->out_height;
     outlink->frame_rate = vpp->framerate;
-    outlink->time_base  = av_inv_q(vpp->framerate);
+    outlink->time_base  = inlink->time_base;
 
     param.filter_frame  = NULL;
     param.num_ext_buf   = 0;