i2c: i2c-smbus: fix i2c_handle_smbus_host_notify documentation

The parameter description is from a previous implementation, update
it to describe the actual implementation.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>