dt: fsl-mma8450.txt: Add missing 'reg' description

Add missing 'reg' description.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
----
 .../devicetree/bindings/input/fsl-mma8450.txt      |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
Signed-off-by: NRob Herring <rob.herring@calxeda.com>

Documentation/devicetree/bindings/input/fsl-mma8450.txt

@@ -2,6 +2,7 @@
 
 Required properties:
 - compatible : "fsl,mma8450".
+- reg: the I2C address of MMA8450
 
 Example: