arm64: dts: exynos: Increase bus frequency for MHL chip

sii8620 supports 1 MHz clock, it allows faster transmissions and according
to extensive tests allows to mitigate some obscure bugs in I2C client
logic of the chip.
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

arch/arm64/boot/dts/exynos/exynos5433-tm2-common.dtsi

@@ -769,6 +769,7 @@ stmfts: touchscreen@49 {
 
 &hsi2c_7 {
 	status = "okay";
+	clock-frequency = <1000000>;
 
 	sii8620@39 {
 		reg = <0x39>;