leds: mt6370: Annotate struct mt6370_priv 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 mt6370_priv.

[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]>
Reviewed-by: AngeloGioacchino Del Regno <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

drivers/leds/flash/leds-mt6370-flash.c

···
 	unsigned int fled_torch_used;
 	unsigned int leds_active;
 	unsigned int leds_count;
-	struct mt6370_led leds[];
+	struct mt6370_led leds[] __counted_by(leds_count);
 };
 
 static int mt6370_torch_brightness_set(struct led_classdev *lcdev, enum led_brightness level)

drivers/leds/rgb/leds-mt6370-rgb.c

···
 	const struct mt6370_pdata *pdata;
 	unsigned int leds_count;
 	unsigned int leds_active;
-	struct mt6370_led leds[];
+	struct mt6370_led leds[] __counted_by(leds_count);
 };
 
 static const struct reg_field common_reg_fields[F_MAX_FIELDS] = {