V4L/DVB (7062): radio-si570x: Some fixes and new USB ID addition

- avoid poss. locking when doing copy_to_user which may sleep
- RDS is automatically activated on read now
- code cleaned of unnecessary rds_commands
- USB Vendor/Product ID for ADS/Tech FM Radio Receiver verified
  (thanks to Guillaume RAMOUSSE)

Signed-off-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>