staging: vc04_services: Use fallthrough pseudo-keyword

Replace the existing /* fall through */ comments and its variants with
the new pseudo-keyword macro fallthrough[1].

[1] https://www.kernel.org/doc/html/v5.7/process/deprecated.html?highlight=fallthrough#implicit-switch-case-fall-throughSigned-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20200727183734.GA28824@embeddedorSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_core.c

@@ -2710,7 +2710,7 @@ vchiq_close_service_internal(struct vchiq_service *service, int close_recvd)
 
 	case VCHIQ_SRVSTATE_OPENSYNC:
 		mutex_lock(&state->sync_mutex);
-		/* fall through */
+		fallthrough;
 	case VCHIQ_SRVSTATE_OPEN:
 		if (close_recvd) {
 			if (!do_abort_bulks(service))