SignalStrength: Hotfix TD-SCDMA take 2

The previous approach worked for 3G, but failed with TD-LTE. Let's
try something different to make them both work, and use the derpy
LTE checks only if a GSM signal is present.

Change-Id: I77e3b5a1e0f99df30c32b102918af418a20077c1
Merge pull request #16 from CyanogenMod/cm-11.0

SignalStrength: Hotfix TD-SCDMA take 2