mtd: rawnand: cadence: Annotate struct cdns_nand_chip 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 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 cdns_nand_chip.

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Roger Quadros <rogerq@kernel.org>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Yang Yingliang <yangyingliang@huawei.com>
Cc: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Valentin Korenblit <vkorenblit@sequans.com>
Cc: ye xingchen <ye.xingchen@zte.com.cn>
Cc: linux-mtd@lists.infradead.org
Cc: linux-hardening@vger.kernel.org
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20231006201734.work.060-kees@kernel.org

drivers/mtd/nand/raw/cadence-nand-controller.c

@@ -526,7 +526,7 @@ struct cdns_nand_chip {
 	/* ECC strength index. */
 	u8 corr_str_idx;
 
-	u8 cs[];
+	u8 cs[] __counted_by(nsels);
 };
 
 struct ecc_info {