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>

mm/page_isolation.c

@@ -286,6 +286,8 @@ __first_valid_page(unsigned long pfn, unsigned long nr_pages)
  * @flags:			isolation flags
  * @gfp_flags:			GFP flags used for migrating pages
  * @isolate_before:	isolate the pageblock before the boundary_pfn
+ * @skip_isolation:	the flag to skip the pageblock isolation in second
+ *			isolate_single_pageblock()
  *
  * Free and in-use pages can be as big as MAX_ORDER-1 and contain more than one
  * pageblock. When not all pageblocks within a page are isolated at the same