xen: add a missing break to the handling of XEN_DOMCTL_getdomaininfo

Thanks to Florian Krohm

From: Ian Campbell <Ian.Campbell@citrix.com>


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13244 a5019735-40e9-0310-863c-91ae7b9d1cf9