This function finds the offset for the given rate in the SHM
- If this is an ODFM Rate
The OFDM Rate Table is located at SHM offset 0x1C0
- If this is a CCK Rate
The CCK Rate Table is located at SHM offset 0x200
- AND the PHY Rate(FIXME) with 0xF and multiply the result by 2
Read SHM at the offset found by combining the Rate Table offset with the Rate index
The offset for this rate in the SHM is the value read multiplied by 2