i2c: i801: Handle SMBAUXCTL_E32B in i801_block_transaction_by_block only

Currently we touch SMBAUXCTL even if not needed. That's the case for block
commands that don't use block buffer mode, either because block buffer
mode isn't available or because it's not supported for the respective
command (e.g. I2C block transfer). Improve this by setting/resetting
SMBAUXCTL_E32B in i801_block_transaction_by_block() only.

Small downside is that we now access SMBAUXCTL twice for transactions
that use PEC and block buffer mode. But this should a rather rare case
and the impact is negligible.

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