clang: suppress warnings

Cast to "char *" explicitly.

    lib/hash.c:1321:16: warning: returning
          'uint8_t [4]' from a function with result type 'char *' converts between
          pointers to integer types with different sign [-Wpointer-sign]
            return entry->io_entry.key.buf;
                   ^~~~~~~~~~~~~~~~~~~~~~~
    lib/hash.c:1327:16: warning: returning
          'uint8_t [8]' from a function with result type 'char *' converts between
          pointers to integer types with different sign [-Wpointer-sign]
            return entry->tiny_entry.key.buf;
                   ^~~~~~~~~~~~~~~~~~~~~~~~~
    lib/hash.c:1334:14: warning: returning
          'uint8_t [4]' from a function with result type 'char *' converts between
          pointers to integer types with different sign [-Wpointer-sign]
          return entry->plain_entry.key;
                 ^~~~~~~~~~~~~~~~~~~~~~
    lib/hash.c:1336:14: warning: returning
          'uint8_t [1]' from a function with result type 'char *' converts between
          pointers to integer types with different sign [-Wpointer-sign]
          return entry->rich_entry.key_and_value;
                 ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/hash.c

@@ -1318,22 +1318,22 @@ grn_hash_entry_get_key(grn_ctx *ctx, grn_hash *hash, grn_hash_entry *entry)
   if (hash->obj.header.flags & GRN_OBJ_KEY_VAR_SIZE) {
     if (grn_hash_is_io_hash(hash)) {
       if (entry->io_entry.flag & HASH_IMMEDIATE) {
-        return entry->io_entry.key.buf;
+        return (char *)entry->io_entry.key.buf;
       } else {
         return (char *)grn_io_hash_key_at(ctx, hash, entry->io_entry.key.offset);
       }
     } else {
       if (entry->tiny_entry.flag & HASH_IMMEDIATE) {
-        return entry->tiny_entry.key.buf;
+        return (char *)entry->tiny_entry.key.buf;
       } else {
         return entry->tiny_entry.key.ptr;
       }
     }
   } else {
     if (hash->key_size == sizeof(uint32_t)) {
-      return entry->plain_entry.key;
+      return (char *)entry->plain_entry.key;
     } else {
-      return entry->rich_entry.key_and_value;
+      return (char *)entry->rich_entry.key_and_value;
     }
   }
 }