mm: use fallthrough;

Convert the various /* fallthrough */ comments to the pseudo-keyword
fallthrough;

Done via script:
https://lore.kernel.org/lkml/b56602fcf79f849e733e7b521bb0e17895d390fa.1582230379.git.joe@perches.com/

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: http://lkml.kernel.org/r/f62fea5d10eb0ccfc05d87c242a620c261219b66.camel@perches.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index c2d7ae6..aabf65d4 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -467,14 +467,14 @@ static int hugetlb_cgroup_read_u64_max(struct seq_file *seq, void *v)
 	switch (MEMFILE_ATTR(cft->private)) {
 	case RES_RSVD_USAGE:
 		counter = &h_cg->rsvd_hugepage[idx];
-		/* Fall through. */
+		fallthrough;
 	case RES_USAGE:
 		val = (u64)page_counter_read(counter);
 		seq_printf(seq, "%llu\n", val * PAGE_SIZE);
 		break;
 	case RES_RSVD_LIMIT:
 		counter = &h_cg->rsvd_hugepage[idx];
-		/* Fall through. */
+		fallthrough;
 	case RES_LIMIT:
 		val = (u64)counter->max;
 		if (val == limit)
@@ -514,7 +514,7 @@ static ssize_t hugetlb_cgroup_write(struct kernfs_open_file *of,
 	switch (MEMFILE_ATTR(of_cft(of)->private)) {
 	case RES_RSVD_LIMIT:
 		rsvd = true;
-		/* Fall through. */
+		fallthrough;
 	case RES_LIMIT:
 		mutex_lock(&hugetlb_limit_mutex);
 		ret = page_counter_set_max(