ARM: shmobile: koelsch: fixup I2C2 clock frequency

Current Koelsch I2C2 has 400kHz settings,
but, ak4643 audio codec chip which is connected to I2C2 can't
work such frequency.
Fixup I2C2 clock frequency to 100kHz.

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