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>

Documentation/devicetree/bindings/leds/leds-lm36274.txt

@@ -6,7 +6,7 @@ up to 29V total output voltage. The 11-bit LED current is programmable via
 the I2C bus and/or controlled via a logic level PWM input from 60 uA to 30 mA.
 
 Parent device properties are documented in
-Documentation/devicetree/bindings/mfd/ti_lmu.txt
+Documentation/devicetree/bindings/mfd/ti-lmu.txt
 
 Regulator properties are documented in
 Documentation/devicetree/bindings/regulator/lm363x-regulator.txt