Fix Order of Operations for Converting RSSI to ASU

Due to the wrong order of operations, the conversion
from RSSI to ASU was returning bad results. Fix the
equation so that the ASU is correctly calculated.

Bug: 126199198
Test: (force device to GSM) - atest CellInfoTest
      verified on aosp_taimen

Change-Id: Iaeb9a2a6d8efb5b39fc1f81e8d2969694cc06422