Printing size_t as %zd instead of %d to suppress warning

```
src/libmaxtouch/info_block.c: In function 'calculate_crc':
src/libmaxtouch/info_block.c:74:3: error: format '%d' expects argument of type 'int', but argument 3 has type 'size_t' [-Werror=format=]
   mxt_verb(mxt->ctx, "Calculating CRC over %d bytes", size);
   ^
cc1: all warnings being treated as errors
```

Suppressed the above warning (which may fail on some systems, depending on GCC configuration) concerning the printing specifier for the variable *size* of type *size_t*. `%zd` should be used instead of `%d` in this instance.