V4L/DVB (3405): Fixes tvp5150a/am1 detection.

- Tvp5150 type were determined by a secondary register instead of
  using ROM code.
- tvp5150am1 have ROM=4.0, while tvp5150a have ROM=3.33 (decimal).
  All other ROM versions are reported as unknown tvp5150.
- Except for reporting, current code doesn't enable any special feature
  for tvp5150am1 or tvp5150a. Code should work for both models (but were
  tested only for tvp5150am1).

Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>