nfit_test: prevent parsing error of nfit_test.0

When you load nfit_test you currently see the following error in dmesg:

 nfit_test nfit_test.0: found a zero length table '0' parsing nfit

This happens because when we parse the nfit_test.0 table via
acpi_nfit_init(), we specify a size of nfit_test->nfit_size.  For the first
pass through nfit_test.0 where (t->setup_hotplug == 0) this is the size of
the entire buffer we allocated, including space for the hot plug
structures, not the size that we've actually filled in.

Fix this by only trying to parse the size of the structures that we've
filled in.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>