ARM: shmobile: r8a7779: add I2C clock for DT

10e8d4f6


(ARM: mach-shmobile: r8a7779: Minimal setup using DT)
added I2C driver for DT, but it didn't add clock.
This patch adds missing clock for I2C

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>