greybus: i2c-gb: convert to use gb_operation_sync

This converts the I2C protocol driver to use gb_operation_sync, removing
lots of places where the create/send/destroy pattern was being used to
send greybus messages.

Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
Reviewed-by: Alex Elder <elder@linaro.org>