upx: fix build error

g++ -O2 -Wall -W -Wcast-align -Wcast-qual -Wpointer-arith -Wshadow -Wwrite-strings -Werror -o compress.o -c compress.cpp
cc1plus: warnings being treated as errors
compress.cpp:75: error: unused parameter 'src'
...

SVN-Revision: 28500