qemu: Remove dead code in qemuDomainAssignPCIAddresses revert patch

qemu: Remove dead code in qemuDomainAssignPCIAddresses revert patch

As it turned out, fix of dead code 419a22 changed the affected condition
from "never true" to "always true", so better fix would be to change the
return code of virDomainMaybeAddController from 0 to 1 if
a new bridge has been added, thus distinguishing case when we didn't need to
add any controller and case we successfully added one.

The return code is changed in the next commit