i965/vec4: Silence unused parameter warnings

i965/vec4: Silence unused parameter warnings

brw_vec4_copy_propagation.cpp:243:59: warning: unused parameter 'reg' [-Wunused-parameter]
                    int arg, struct copy_entry *entry, int reg)
                                                           ^

brw_vec4_generator.cpp:869:57: warning: unused parameter 'inst' [-Wunused-parameter]
 vec4_generator::generate_unpack_flags(vec4_instruction *inst,
                                                         ^

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>