tty: rocket: Fix possible buffer overwrite on register_PCI

If number of isa and pci boards exceed NUM_BOARDS on the path
rp_init()->init_PCI()->register_PCI() then buffer overwrite occurs
in register_PCI() on assign rcktpt_io_addr[i].

The patch adds check on upper bound for index of registered
board in register_PCI.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Anton Vasilyev <vasilyev@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/rocket.c

@@ -1881,7 +1881,7 @@ static __init int register_PCI(int i, struct pci_dev *dev)
 	ByteIO_t UPCIRingInd = 0;
 
 	if (!dev || !pci_match_id(rocket_pci_ids, dev) ||
-	    pci_enable_device(dev))
+	    pci_enable_device(dev) || i >= NUM_BOARDS)
 		return 0;
 
 	rcktpt_io_addr[i] = pci_resource_start(dev, 0);