serial: tegra20-hsuart: Fix typo in dmas DT binding description

The description for dmas references a second property, which should be
"dma-names" instead of "clock-names".
Signed-off-by: NMirza Krak <mirza.krak@gmail.com>
Acked-by: NRob Herring <robh@kernel.org>
Signed-off-by: NThierry Reding <treding@nvidia.com>

Documentation/devicetree/bindings/serial/nvidia,tegra20-hsuart.txt

@@ -10,7 +10,7 @@ Required properties:
   See ../reset/reset.txt for details.
 - reset-names : Must include the following entries:
   - serial
-- dmas : Must contain an entry for each entry in clock-names.
+- dmas : Must contain an entry for each entry in dma-names.
   See ../dma/dma.txt for details.
 - dma-names : Must include the following entries:
   - rx