mm/page_isolation.c: fix one kernel-doc comment

Remove one warning found by running scripts/kernel-doc, which is caused by
using 'make W=1':

mm/page_isolation.c:304: warning: Function parameter or member
'skip_isolation' not described in 'isolate_single_pageblock'

Link: https://lkml.kernel.org/r/20220602062116.61199-1-yang.lee@linux.alibaba.com


Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>