xenpaging: do not leak if --pagefile given twice

By freeing filename (which is either NULL or the previous iteration of
this argument). This implements a semantic where the last --pagefile
given on the command line takes precedence.

This is the same semantic as the other options have.

CID: 1198792

Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Ian Campbell <ian.campbell@citrix.com>

tools/xenpaging/xenpaging.c

@@ -232,6 +232,7 @@ static int xenpaging_getopts(struct xenpaging *paging, int argc, char *argv[])
             paging->vm_event.domain_id = atoi(optarg);
             break;
         case 'f':
+            free(filename);
             filename = strdup(optarg);
             break;
         case 'm':