i2c: ibm_iic: don't check number of messages in the driver

Since commit 1eace834 ("i2c: add param sanity check to
i2c_transfer()"), the I2C core does this check now. We can remove it
from drivers.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Reviewed-by: Peter Rosin <peda@axentia.se>