i2c: i801: Replace waitqueue with completion API

Using the completion API is more intuitive and it allows to simplify
the code. Note that we don't have to set priv->status = 0 any longer
with the completion API.

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