radio: tavarua: Use proper length to read the data

- Copies the entire 16 bytes including the unused last
  byte of RX_STATIONS_0.
- Userspace will get wrong frequency.
- Use proper length to read the data when HOST receives search list event.

Change-Id: I69ecc01c327c4f803dd594a95ca539339bdec574
CRs-Fixed: 468619
Signed-off-by: Venkateshwarlu Domakonda <Venkateshwarlu@codeaurora.org>