Nokia RX-51: Decrease i2c speed to 100000

It looks like that i2c bus lot of times timeout on some units. Prior
migration to CONFIG_DM_I2C i2c speed was set to CONFIG_SYS_OMAP24_I2C_SPEED
value which was 100000. Lower speed fixes timeout problems, so change speed
back to its previous value.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: 8d8c1817 ("Nokia RX-51: Convert to CONFIG_DM_I2C")
Reviewed-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>