libxl: add missing "break;" to do_pci_remove

Otherwise we erroneously fall through the LIBXL_DOMAIN_TYPE_PV case into the
"default: abort()".

(I'm sure we fixed this once already...)

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Tested-by: Dario Faggioli <dario.faggioli@citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/libxl_pci.c

@@ -930,6 +930,7 @@ skip1:
             }
         }
         fclose(f);
+        break;
     }
     default:
         abort();