greybus: vibrator-gb: convert to use gb_operation_sync

This converts the vibrator protocol driver to use gb_operation_sync,
removing the hand-rolled version of the same function, as well as
removing an open-coded version for a request when turning on the
vibrator motor.

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