leds: simatic-ipc-leds-gpio: Add terminating entries to gpio tables

The entries do not seem to be stricly needed when the number of entries
is given via the number of LEDs. But adding them is a safeguard should
anyone ever iterate over the tables to their end, it also gets us in
line with other drivers that register "leds-gpio" tables.

Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Henning Schild <henning.schild@siemens.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230524124628.32295-2-henning.schild@siemens.com