Fix build.

Bring xc_mem_paging.c in line with other users of munlock in libxc.
Otherwise it trips over -Werror=unused-value

Signed-off-by: Tim Deegan <tim@xen.org>

tools/libxc/xc_mem_paging.c

@@ -87,7 +87,7 @@ int xc_mem_paging_load(xc_interface *xch, domid_t domain_id,
                                 buffer, NULL, gfn);
 
     old_errno = errno;
-    munlock(buffer, XC_PAGE_SIZE);
+    (void) munlock(buffer, XC_PAGE_SIZE);
     errno = old_errno;
 
     return rc;