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

Add missing 'reg' description.

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