firewire: add CSR CYCLE_TIME write support

The specification requires that CYCLE_TIME is writable so that it can be
initialized, so we better implement it.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

drivers/firewire/core-transaction.c

@@ -1097,6 +1097,9 @@ static void handle_registers(struct fw_card *card, struct fw_request *request,
 		if (TCODE_IS_READ_REQUEST(tcode) && length == 4)
 			*data = cpu_to_be32(card->driver->
 					read_csr_reg(card, CSR_CYCLE_TIME));
+		else if (tcode == TCODE_WRITE_QUADLET_REQUEST)
+			card->driver->write_csr_reg(card, CSR_CYCLE_TIME,
+						    be32_to_cpu(*data));
 		else
 			rcode = RCODE_TYPE_ERROR;
 		break;