dt-bindings: mfd: zii,rave-sp: Fix a typo ("onborad")

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/mfd/zii,rave-sp.txt

@@ -20,7 +20,7 @@ RAVE SP consists of the following sub-devices:
 Device				 Description
 ------				 -----------
 rave-sp-wdt			: Watchdog
-rave-sp-nvmem			: Interface to onborad EEPROM
+rave-sp-nvmem			: Interface to onboard EEPROM
 rave-sp-backlight		: Display backlight
 rave-sp-hwmon			: Interface to onboard hardware sensors
 rave-sp-leds			: Interface to onboard LEDs