pc-bios/s390-ccw/net: fix a possible memory leak in get_uuid()

There is a possible memory leak in get_uuid(). Should free allocated mem
before
return NULL.

Signed-off-by: Yifan Luo <luoyifan@cmss.chinamobile.com>
Message-Id: <02cf01d55267$86cf2850$946d78f0$@cmss.chinamobile.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

pc-bios/s390-ccw/netmain.c

@@ -269,6 +269,7 @@ static const char *get_uuid(void)
                  : "d" (r0), "d" (r1), [addr] "a" (buf)
                  : "cc", "memory");
     if (cc) {
+        free(mem);
         return NULL;
     }