leds: aw200xx: Annotate struct aw200xx 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 aw200xx.

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

Signed-off-by: Kees Cook <[e-mail]>
Reviewed-by: Gustavo A. R. Silva <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/leds-aw200xx.c

···
 	struct mutex mutex;
 	u32 num_leds;
 	u32 display_rows;
-	struct aw200xx_led leds[];
+	struct aw200xx_led leds[] __counted_by(num_leds);
 };
 
 static ssize_t dim_show(struct device *dev, struct device_attribute *devattr,