dt: leds-lm36274.txt: fix a broken reference to ti-lmu.txt

There's a typo there:
	ti_lmu.txt -> ti-lmu.txt

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>