Qualcomm LTE RILs: do not make mLteRsrp negative

  * In CM10.1, SignalStrength::validateInput() was added. This function expects
    mLteRsrp to be positive coming from the RIL.
  * Inverting in the RIL was causing validateInput() to flag mLteRsrp as invalid.
  * This shows up as a 0x7fffffff in About phone->Status->Signal strength when on LTE
  * Let validateInput() invert the sign instead of doing it in the custom RILs

Change-Id: I6ae7e4a56141c49628576305d21bee77b2a93ad7