greybus: svc: Use 'dev' instead '&op->connection->dev'

We already have a variable to access '&op->connection->dev' directly,
lets reuse it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Jean Pihet <jean.pihet@newoldbits.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>