dt-bindings: i2c: nvidia,tegra20-i2c: restrict also clocks in if:then:

Both xxx and xxx-names properties with variable number of items should
be constrained in each "if:then:".  Add missing constraints for clocks,
since we have such for clock-names.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>