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>

drivers/usb/host/xhci.c

@@ -4618,7 +4618,7 @@ static unsigned long long xhci_calculate_intel_u1_timeout(
 			break;
 		}
 		/* Otherwise the calculation is the same as isoc eps */
-		/* fall through */
+		fallthrough;
 	case USB_ENDPOINT_XFER_ISOC:
 		timeout_ns = xhci_service_interval_to_ns(desc);
 		timeout_ns = DIV_ROUND_UP_ULL(timeout_ns * 105, 100);