lavd/v4l2: allow devices not implementing VIDIOC_G_PARM

Not all v4l2 devices implement the VIDIOC_G_PARM ioctl. This patch allow
ffmpeg to open such device and treat it the same as devices that do
implement the ioctl but returns that it do not implement the
V4L2_CAP_TIMEPERFRAME capability.

Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Benoit Fouet <benoit.fouet@free.fr>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavdevice/v4l2.c

@@ -715,11 +715,8 @@ static int v4l2_set_parameters(AVFormatContext *ctx)
     streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     if (v4l2_ioctl(s->fd, VIDIOC_G_PARM, &streamparm) < 0) {
         ret = AVERROR(errno);
-        av_log(ctx, AV_LOG_ERROR, "ioctl(VIDIOC_G_PARM): %s\n", av_err2str(ret));
-        return ret;
-    }
-
-    if (framerate_q.num && framerate_q.den) {
+        av_log(ctx, AV_LOG_WARNING, "ioctl(VIDIOC_G_PARM): %s\n", av_err2str(ret));
+    } else if (framerate_q.num && framerate_q.den) {
         if (streamparm.parm.capture.capability & V4L2_CAP_TIMEPERFRAME) {
             tpf = &streamparm.parm.capture.timeperframe;