mtd: rawnand: renesas: Annotate struct rnand_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 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 rnand_chip.

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

Cc: Miquel Raynal <[e-mail]>
Cc: Richard Weinberger <[e-mail]>
Cc: Vignesh Raghavendra <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: Gustavo A. R. Silva <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

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

···
 	u32 tim_gen_seq1;
 	u32 tim_gen_seq2;
 	u32 tim_gen_seq3;
-	struct rnand_chip_sel sels[];
+	struct rnand_chip_sel sels[] __counted_by(nsels);
 };
 
 struct rnandc {