mach-mx5: fix the I2C clock parents

mach-mx5: fix the I2C clock parents

The clock from which the I2C timing is derived is the ipg_perclk not ipg_clk.

I2C bus frequency was lower by a factor of ~8 due to the clock divider
calculation being based on 66.5MHz IPG clock while the bus actually
uses 8MHz ipg_perclk.

Kernel version: 3.0.0-rc2 branch 'imx-for-next' of git://git.pengutronix.de/git/imx/linux-2.6

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>