Use the fallthrough statement in switch loops

Clang does not seem to work with 'fall through' in comments.

Change-Id: Idcbe373be33ef7247548f856bfaba7ceb7f749b5
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/51498
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>

src/lib/dp_aux.c

@@ -20,13 +20,13 @@ enum i2c_over_aux dp_get_aux_cmd(enum aux_request request, uint32_t remaining_af
 	case I2C_RAW_WRITE_AND_STOP:
 		if (!remaining_after_this)
 			return I2C_OVER_AUX_WRITE_MOT_0;
-		/* fallthrough */
+		__fallthrough;
 	case I2C_RAW_WRITE:
 		return I2C_OVER_AUX_WRITE_MOT_1;
 	case I2C_RAW_READ_AND_STOP:
 		if (!remaining_after_this)
 			return I2C_OVER_AUX_READ_MOT_0;
-		/* fallthrough */
+		__fallthrough;
 	case I2C_RAW_READ:
 		return I2C_OVER_AUX_READ_MOT_1;
 	case DPCD_WRITE:

src/lib/edid.c

@@ -1183,13 +1183,13 @@ int decode_edid(unsigned char *edid, int size, struct edid *out)
 		switch (edid[0x13]) {
 		case 4:
 			c.claims_one_point_four = 1;
-			/* fall through */
+			__fallthrough;
 		case 3:
 			c.claims_one_point_three = 1;
-			/* fall through */
+			__fallthrough;
 		case 2:
 			c.claims_one_point_two = 1;
-			/* fall through */
+			__fallthrough;
 		default:
 			c.claims_one_point_oh = 1;
 		}

src/lib/prog_loaders.c

@@ -167,7 +167,8 @@ void payload_load(void)
 		if (CONFIG(PAYLOAD_FIT_SUPPORT)) {
 			fit_payload(payload, mapping);
 			break;
-		} /* else fall-through */
+		}
+		__fallthrough;
 	default:
 		die_with_post_code(POST_INVALID_ROM,
 				   "Unsupported payload type %d.\n", payload->cbfs_type);