msc/BSC_ConnectionHandler: fix early return in f_mm_ciph_geran()

In [1] I forgot to invert an if statement.  This regression caused
most of GERAN specific test cases to fail due to "Tguard timeout".

Change-Id: I8cbaff00abfd9eb252dc3011df848e2e24fe5a1e
Fixes: [1] Ib7ebe8fd675295beb02cadebb19d8465dffeb732
Related: OS#5333
1 file changed