ata: libata: Annotate struct ata_cpr_log 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 ata_cpr_log.

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

Cc: Damien Le Moal <dlemoal@kernel.org>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>

include/linux/libata.h

@@ -656,7 +656,7 @@ struct ata_cpr {
 
 struct ata_cpr_log {
 	u8			nr_cpr;
-	struct ata_cpr		cpr[];
+	struct ata_cpr		cpr[] __counted_by(nr_cpr);
 };
 
 struct ata_device {