ARM: OMAP: Fix i2c init for twl4030

Looks like 2600 kHz rate does not work reliably on 2430,
so just use the 100 kHz rate.

Otherwise the system often fails to boot properly with:

omap_i2c omap_i2c.2: timeout waiting for bus ready
omap_i2c omap_i2c.2: timeout waiting for bus ready
twl: i2c_write failed to transfer all messages
omap_i2c omap_i2c.2: timeout waiting for bus ready
twl: i2c_write failed to transfer all messages
omap_i2c omap_i2c.2: timeout waiting for bus ready
twl: i2c_write failed to transfer all messages
twl: clock init err [-110]
omap_i2c omap_i2c.2: timeout waiting for bus ready
twl: i2c_write failed to transfer all messages
TWL4030 Unable to unlock IDCODE registers --110

Signed-off-by: Tony Lindgren <tony@atomide.com>