mm/kasan/init.c: fix doc warning

Fix gcc W=1 warning:

  mm/kasan/init.c:228: warning: Function parameter or member 'shadow_start' not described in 'kasan_populate_early_shadow'
  mm/kasan/init.c:228: warning: Function parameter or member 'shadow_end' not described in 'kasan_populate_early_shadow'

Link: https://lkml.kernel.org/r/20210603140700.3045298-1-yukuai3@huawei.com
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Cc: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: YuKuai-huawei

mm/kasan/init.c

@@ -220,8 +220,8 @@ static int __ref zero_p4d_populate(pgd_t *pgd, unsigned long addr,
 /**
  * kasan_populate_early_shadow - populate shadow memory region with
  *                               kasan_early_shadow_page
- * @shadow_start - start of the memory range to populate
- * @shadow_end   - end of the memory range to populate
+ * @shadow_start: start of the memory range to populate
+ * @shadow_end: end of the memory range to populate
  */
 int __ref kasan_populate_early_shadow(const void *shadow_start,
 					const void *shadow_end)