gpio: ljca: Initialize num before accessing item in ljca_gpio_config

gpio: ljca: Initialize num before accessing item in ljca_gpio_config

With the new __counted_by annocation in ljca_gpio_packet, the "num"
struct member must be set before accessing the "item" array. Failing to
do so will trigger a runtime warning when enabling CONFIG_UBSAN_BOUNDS
and CONFIG_FORTIFY_SOURCE.

Fixes: 1034cc423f1b ("gpio: update Intel LJCA USB GPIO driver")
Cc: stable@vger.kernel.org
Signed-off-by: Haoyu Li <lihaoyu499@gmail.com>
Link: https://lore.kernel.org/stable/20241203141451.342316-1-lihaoyu499%40gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>