qemu: handle USB bus in qemuAssignDeviceDiskAliasFixed()
qemu: handle USB bus in qemuAssignDeviceDiskAliasFixed()

The qemuAssignDeviceDiskAliasFixed() method was missing handling
for the USB disk bus type.

Signed-off-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

zippy2/libvirt,rlaager/libvirt,nertpinx/libvirt,eskultety/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,taget/libvirt,fabianfreyer/libvirt,eskultety/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,libvirt/libvirt,crobinso/libvirt,datto/libvirt,nertpinx/libvirt,jfehlig/libvirt,rlaager/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,rlaager/libvirt,rlaager/libvirt,datto/libvirt,taget/libvirt,datto/libvirt,jardasgit/libvirt,andreabolognani/libvirt,crobinso/libvirt,andreabolognani/libvirt,nertpinx/libvirt,libvirt/libvirt,jardasgit/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,eskultety/libvirt,jfehlig/libvirt,eskultety/libvirt,zippy2/libvirt,taget/libvirt,taget/libvirt,datto/libvirt,zippy2/libvirt,andreabolognani/libvirt,crobinso/libvirt,jardasgit/libvirt,olafhering/libvirt,crobinso/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,taget/libvirt,fabianfreyer/libvirt,rlaager/libvirt,datto/libvirt,olafhering/libvirt,nertpinx/libvirt,eskultety/libvirt,libvirt/libvirt,jfehlig/libvirt,jardasgit/libvirt