leds: syscon: Get rid of custom led_init_default_state_get()

LED core provides a helper to parse default state from firmware node.
Use it instead of custom implementation.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230103131256.33894-11-andriy.shevchenko@linux.intel.com