greybus: fix vibrator request_operation()

And this fixes a problem similar the last two, this time found in
the vibrator protcool driver code.

Change a variable name in get_version() to reflect that it holds
a response message, not a request message.

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