media: mgb4: Fixed signal frame rate limit handling

Change the default DV timings for the outputs to produce a better signal
less "crippled" by the frame rate limiting. While the individual values
are now different, the resulting signal still matches the same default
display as before.

Additionally fix the corner case when the frame rate limit is set to zero
causing a "divide by zero" kernel panic.

Signed-off-by: Martin Tůma <martin.tuma@digiteqautomotive.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>