Tidy up some of the warn_report() messages after having converted them
to use warn_report().

Signed-off-by: Alistair Francis <alistair.francis@xilinx.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <9cb1d23551898c9c9a5f84da6773e99871285120.1505158760.git.alistair.francis@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>