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

Since commit 1eace834 ("i2c: add param sanity check to
i2c_transfer()") and b7f62584 ("i2c: add quirk checks to core"), the
I2C core does this check now. We can remove it here.

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