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/iio/health/max30102.c b/drivers/iio/health/max30102.c
index 9b47d94..d9b2ed8 100644
--- a/drivers/iio/health/max30102.c
+++ b/drivers/iio/health/max30102.c
@@ -273,10 +273,10 @@ static int max30102_read_measurement(struct max30102_data *data,
 	switch (measurements) {
 	case 3:
 		MAX30102_COPY_DATA(2);
-		/* fall through */
+		fallthrough;
 	case 2:
 		MAX30102_COPY_DATA(1);
-		/* fall through */
+		fallthrough;
 	case 1:
 		MAX30102_COPY_DATA(0);
 		break;