leds: simatic-ipc-leds: Make simatic_ipc_led_mem_res static

simatic_ipc_led_mem_res is not used outside of the driver, make it static.

Cc: Henning Schild <henning.schild@siemens.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>