iio: proximity: hx9023s: fix assignment order for __counted_by

iio: proximity: hx9023s: fix assignment order for __counted_by

Initialize fw_size before copying firmware data into the flexible
array member to match the __counted_by() annotation. This fixes the
incorrect assignment order that triggers runtime safety checks.

Fixes: e9ed97be4fcc ("iio: proximity: hx9023s: Added firmware file parsing functionality")
Signed-off-by: Yasin Lee <yasin.lee.x@gmail.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>