lib: Fix RXVGA1 set/get to convert from dB to raw value

The formula used is a very crude quadratic approximation from the
3 data points given in the programming manual ... for something more
precise, we'd need a LUT. But it may vary with temp and device anyway.

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
lib: Fix TXVGA2/RXVGA2, avoid casting (int*) to (uint8_t *)

Not everyone is little endian !

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
Merge pull request #23 from smunaut/lib_fixes

Lib fixes