leds: max77650: Remove set but not used variable 'parent'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/leds/leds-max77650.c: In function max77650_led_probe:
drivers/leds/leds-max77650.c:67:17: warning: variable parent set but not used [-Wunused-but-set-variable]

It is never used and can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>