drm/syncobj: fix DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE

If DRM_IOCTL_SYNCOBJ_TIMELINE_WAIT is invoked with the
DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE flag set but no fence has yet been
submitted for the given timeline point the call will fail immediately
with EINVAL. This does not match the intended behavior where the call
should wait until the fence has been submitted (or the timeout expires).

The following small example program illustrates the issue. It should
wait for 5 seconds and then print ETIME, but instead it terminates right
away after printing EINVAL.

  #include <stdio.h>
  #include <fcntl.h>
  #include <time.h>
  #include <errno.h>
  #include <xf86drm.h>
  int main(void)
  {
      int fd = open("/dev/dri/card0", O_RDWR);
      uint32_t syncobj;
      drmSyncobjCreate(fd, 0, &syncobj);
      struct timespec ts;
      clock_gettime(CLOCK_MONOTONIC, &ts);
      uint64_t point = 1;
      if (drmSyncobjTimelineWait(fd, &syncobj, &point, 1,
                                 ts.tv_sec * 1000000000 + ts.tv_nsec + 5000000000, // 5s
                                 DRM_SYNCOBJ_WAIT_FLAGS_WAIT_AVAILABLE, NULL)) {
          printf("drmSyncobjTimelineWait failed %d\n", errno);
      }
  }

Fixes: 01d6c357

 ("drm/syncobj: add support for timeline point wait v8")
Signed-off-by: Erik Kurzinger <ekurzinger@nvidia.com>
Reviewed by: Simon Ser <contact@emersion.fd>
Signed-off-by: Simon Ser <contact@emersion.fr>
Link: https://patchwork.freedesktop.org/patch/msgid/1fac96f1-2f3f-f9f9-4eb0-340f27a8f6c0@nvidia.com