spapr: add missing break in h_get_cpu_characteristics()
    
    Detected by Coverity (CID 1385702). This fixes the recently added hypercall
    to let guests properly apply Spectre and Meltdown workarounds.
    
    Fixes: c59704b25473 "target/ppc/spapr: Add H-Call H_GET_CPU_CHARACTERISTICS"
    Reported-by: Paolo Bonzini <pbonzini@redhat.com>
    Signed-off-by: Greg Kurz <groug@kaod.org>
    Reviewed-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
    Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
    (cherry picked from commit fa86f59234919b479b7e8da6b0dc2dad894a5eac)
    Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>