libxl: fix double free at get_all_assigned_devices

Do not free() list manually - it will be freed by libxl__free_all.

Signed-off-by: Marek Marczykowski <marmarek@mimuw.edu.pl>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/libxl_pci.c

@@ -469,7 +469,6 @@ static int get_all_assigned_devices(libxl__gc *gc, libxl_device_pci **list, int
     }
 
     if ( 0 == *num ) {
-        free(pcidevs);
         pcidevs = NULL;
     }else{
         *list = pcidevs;