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>