Fixes this compiler warning:

drivers/media/test-drivers/vivid/vivid-core.c: In function 'vidioc_querycap':
drivers/media/test-drivers/vivid/vivid-core.c:243:35: warning: '%s' directive output may be truncated writing up to 35 bytes into a region of size 23 [-Wformat-truncation=]
  243 |                         "platform:%s", dev->v4l2_dev.name);
      |                                   ^~
drivers/media/test-drivers/vivid/vivid-core.c:242:9: note: 'snprintf' output between 10 and 45 bytes into a destination of size 32
  242 |         snprintf(cap->bus_info, sizeof(cap->bus_info),
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  243 |                         "platform:%s", dev->v4l2_dev.name);
      |                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>