build: Fix a gcc 4.2 warning on 64bit systems

src/descrambler/capmt.c:485: warning: comparison is always false due to limited range of data type
src/descrambler/capmt.c:487: warning: comparison is always false due to limited range of data type
src/descrambler/capmt.c:538: warning: comparison is always false due to limited range of data type
src/descrambler/capmt.c:549: warning: comparison is always false due to limited range of data type