Add Missing getRssi to CellSignalStrengthGsm

The getRssi() method is missing. This should
be used in consistency with the rest of the
CellSignalStrength interface, which provides
explicitly named measurement results through
such getters.

Bug: 125027693
Test: compilation
Change-Id: Ib7485118967108c066af40f811ad934b8de771f8
1 file changed