Add a missing comma in Vendor Methods of Developer Guide
Add a missing comma in Vendor Methods of Developer Guide

This patch added a missing comma to the vendor passthru sample code in
Vendor Methods of Developer Guide so that the sample can be used for a
template.

Change-Id: I8d224714e4e177073239fdfe44ed3d1e31ddba30

ionutbalutoiu/ironic,SauloAislan/ironic,dims/ironic,naterh/ironic,pshchelo/ironic,bacaldwell/ironic,openstack/ironic,pshchelo/ironic,redhat-openstack/ironic,ionutbalutoiu/ironic,hpproliant/ironic,NaohiroTamura/ironic,SauloAislan/ironic,bacaldwell/ironic,devananda/ironic,NaohiroTamura/ironic,dims/ironic,openstack/ironic,Tan0/ironic