Fill in bus_info with fixed name.

This fixes this compiler warning:

drivers/media/radio/radio-miropcm20.c: In function 'vidioc_querycap':
drivers/media/radio/radio-miropcm20.c:206:57: warning: '%s' directive output may be truncated writing up to 35 bytes into a region of size 28 [-Wformat-truncation=]
  206 |         snprintf(v->bus_info, sizeof(v->bus_info), "ISA:%s", dev->v4l2_dev.name);
      |                                                         ^~
drivers/media/radio/radio-miropcm20.c:206:9: note: 'snprintf' output between 5 and 40 bytes into a destination of size 32
  206 |         snprintf(v->bus_info, sizeof(v->bus_info), "ISA:%s", dev->v4l2_dev.name);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>