in_table_factory.cc: use correct format specifier

Use %zu instead of %zd since size_t and uint32_t are unsigned.

Fix for:

[table/plain_table_factory.cc:55]: (warning) %zd in format string (no. 1)
 requires 'ssize_t' but the argument type is 'size_t {aka unsigned long}'.
[table/plain_table_factory.cc:58]: (warning) %zd in format string (no. 1)
 requires 'ssize_t' but the argument type is 'size_t {aka unsigned long}'.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>