nir: Silence unused parameter warnings

nir: Silence unused parameter warnings

nir/nir.h: In function 'nir_validate_shader':
nir/nir.h:1567:56: warning: unused parameter 'shader' [-Wunused-parameter]
 static inline void nir_validate_shader(nir_shader *shader) { }
                                                        ^
nir/nir_opt_cse.c: In function 'src_is_ssa':
nir/nir_opt_cse.c:165:32: warning: unused parameter 'data' [-Wunused-parameter]
 src_is_ssa(nir_src *src, void *data)
                                ^
nir/nir_opt_cse.c: In function 'dest_is_ssa':
nir/nir_opt_cse.c:171:35: warning: unused parameter 'data' [-Wunused-parameter]
 dest_is_ssa(nir_dest *dest, void *data)
                                   ^

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Connor Abbott <cwabbott0@gmail.com>