i2c: i801: Centralize configuring block commands in i801_block_transaction

Similar to what was done for non-block commands, centralize block
command register settings in i801_block_transaction().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>