intel/compiler: Silence unused parameter warning in fs_live_variables::setup_one_read

intel/compiler: Silence unused parameter warning in fs_live_variables::setup_one_read

src/intel/compiler/brw_fs_live_variables.cpp: In member function ‘void brw::fs_live_variables::setup_one_read(brw::fs_live_variables::block_data*, fs_inst*, int, const fs_reg&)’:
src/intel/compiler/brw_fs_live_variables.cpp:56:67: warning: unused parameter ‘inst’ [-Wunused-parameter]
   56 | fs_live_variables::setup_one_read(struct block_data *bd, fs_inst *inst,
      |                                                          ~~~~~~~~~^~~~

Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4582>