i2c: i801: Prefer async probe

This i801 driver probe can take more than ~190ms in some devices, since
the "i2c_register_spd()" call was added inside
"i801_probe_optional_slaves()".

Prefer async probe so that other drivers can be probed and boot can
continue in parallel while this driver loads, to reduce boot time. There is
no reason to block other drivers from probing while this driver is
loading.

Signed-off-by: Mani Milani <mani@chromium.org>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@kernel.org>