Use a %postun -p for one line scriptlet

Changed by Rich Jones, presumably for this:

  libvirt.x86_64: W: one-line-command-in-%postun /sbin/ldconfig

see:

  https://bugzilla.redhat.com/226055

libvirt.spec.in

@@ -436,8 +436,7 @@ if [ $1 = 0 ]; then
 fi
 %endif
 
-%postun
-/sbin/ldconfig
+%postun -p /sbin/ldconfig
 
 %files
 %defattr(-, root, root)