serial: 8250_pci1xxxx: Annotate struct pci1xxxx_8250 with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
(for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct pci1xxxx_8250.

[1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci

Cc: Kumaravel Thiagarajan <[email protected]>
Cc: Tharun Kumar P <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Jiri Slaby <[email protected]>
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: "Gustavo A. R. Silva" <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: kees

drivers/tty/serial/8250/8250_pci1xxxx.c

@@ -107,7 +107,7 @@ static const int logical_to_physical_port_idx[][MAX_PORTS] = {
 struct pci1xxxx_8250 {
 	unsigned int nr;
 	void __iomem *membase;
-	int line[];
+	int line[] __counted_by(nr);
 };
 
 static int pci1xxxx_get_num_ports(struct pci_dev *dev)