leds: lgm-sso: Convert to use list_for_each_entry*() API

Convert to use list_for_each_entry*() API insted of open coded variants.
It saves few lines of code and makes iteasier to read and maintain.

Signed-off-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>