eeprom: at24: Annotate struct at24_data 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 at24_data.

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

Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

drivers/misc/eeprom/at24.c

@@ -92,7 +92,7 @@ struct at24_data {
 	 * them for us.
 	 */
 	u8 bank_addr_shift;
-	struct regmap *client_regmaps[];
+	struct regmap *client_regmaps[] __counted_by(num_addresses);
 };
 
 /*