Let the V4L2 core fill in bus_info.

This fixes this warning:

drivers/media/radio/radio-si476x.c: In function 'si476x_radio_querycap':
drivers/media/radio/radio-si476x.c:333:28: warning: '%s' directive output may be truncated writing up to 35 bytes into a region of size 23 [-Wformat-truncation=]
  333 |                  "platform:%s", radio->v4l2dev.name);
      |                            ^~
drivers/media/radio/radio-si476x.c:332:9: note: 'snprintf' output between 10 and 45 bytes into a destination of size 32
  332 |         snprintf(capability->bus_info, sizeof(capability->bus_info),
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  333 |                  "platform:%s", radio->v4l2dev.name);
      |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>