clang: suppress a warning
clang: suppress a warning

Add a missing cast.

    lib/token.c:435:54: warning: passing
          'const unsigned char *' to parameter of type 'const char *' converts
          between pointers to integer types with different sign [-Wpointer-sign]
      grn_tokenizer_token_push(ctx, &(tokenizer->token), p, r - p, status);
                                                         ^
    include/groonga/tokenizer.h:183:61: note:
          passing argument to parameter 'str_ptr' here
      ...const char *str_ptr, unsigned int str_length,
                     ^

groonga/groonga,cosmo0920/groonga,groonga/groonga,cosmo0920/groonga,hiroyuki-sato/groonga,kenhys/groonga,komainu8/groonga,myokoym/groonga,naoa/groonga,cosmo0920/groonga,kenhys/groonga,kenhys/groonga,hiroyuki-sato/groonga,redfigure/groonga,kenhys/groonga,hiroyuki-sato/groonga,hiroyuki-sato/groonga,naoa/groonga,naoa/groonga,redfigure/groonga,redfigure/groonga,myokoym/groonga,komainu8/groonga,redfigure/groonga,groonga/groonga,myokoym/groonga,naoa/groonga,kenhys/groonga,hiroyuki-sato/groonga,naoa/groonga,naoa/groonga,komainu8/groonga,kenhys/groonga,komainu8/groonga,cosmo0920/groonga,redfigure/groonga,myokoym/groonga,hiroyuki-sato/groonga,komainu8/groonga,cosmo0920/groonga,redfigure/groonga,kenhys/groonga,komainu8/groonga,kenhys/groonga,groonga/groonga,groonga/groonga,groonga/groonga,myokoym/groonga,myokoym/groonga,cosmo0920/groonga,hiroyuki-sato/groonga,groonga/groonga,cosmo0920/groonga,naoa/groonga,cosmo0920/groonga,myokoym/groonga,komainu8/groonga,groonga/groonga,redfigure/groonga,hiroyuki-sato/groonga,redfigure/groonga,komainu8/groonga,naoa/groonga,myokoym/groonga