drivers: display: ls0xx: fix compiler warning

Fix a compiler warning introduced in 0fa2c450:

/zephyr/drivers/display/ls0xx.c: In function 'ls0xx_init':
/zephyr/drivers/display/ls0xx.c:294:9: error: passing argument 5 of
'k_thread_create' discards 'const' qualifier from pointer target type
[-Werror=discarded-qualifiers]
  294 |         config, NULL, NULL,
      |         ^~~~~~

Signed-off-by: Fabio Baltieri <fabio.baltieri@gmail.com>