altos/cc1200: Adjust bit-sync configuration

The default bit timing adjustment mechanism allows for only a 0.2%
deviation from the programmed bit timing. I found one TeleMini device
which is beyond that tolerance as it was built with an older crystal
with more error.

Switch to the more expensive synchronization mechanism which allows up
to 2% timing error, but requires a multi-byte preamble (which we
have). This fixes packet mode nicely.

Signed-off-by: Keith Packard <keithp@keithp.com>