ACPI: NFIT: Fix flexible_array.cocci warnings

Julia and 0day report:

    Zero-length and one-element arrays are deprecated, see
    Documentation/process/deprecated.rst
    Flexible-array members should be used instead.

However, a straight conversion to flexible arrays yields:

    drivers/acpi/nfit/core.c:2276:4: error: flexible array member in a struct with no named members
    drivers/acpi/nfit/core.c:2287:4: error: flexible array member in a struct with no named members

Instead, just use plain arrays not embedded flexible arrays.

Cc: Denis Efremov <efremov@linux.com>
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>