treewide: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1]. Also, remove unnecessary
fall-through markings when it is the case.

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-through

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
diff --git a/drivers/hwmon/emc1403.c b/drivers/hwmon/emc1403.c
index cf0962f..e9c0bbc 100644
--- a/drivers/hwmon/emc1403.c
+++ b/drivers/hwmon/emc1403.c
@@ -406,10 +406,10 @@ static int emc1403_probe(struct i2c_client *client,
 	switch (id->driver_data) {
 	case emc1404:
 		data->groups[2] = &emc1404_group;
-		/* fall through */
+		fallthrough;
 	case emc1403:
 		data->groups[1] = &emc1403_group;
-		/* fall through */
+		fallthrough;
 	case emc1402:
 		data->groups[0] = &emc1402_group;
 	}