regulator: da9063: Annotate struct da9063_regulators 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 da9063_regulators.

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

Cc: Support Opensource <support.opensource@diasemi.com>
Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230922175207.work.576-kees@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/da9063-regulator.c

@@ -158,7 +158,7 @@ struct da9063_regulator {
 struct da9063_regulators {
 	unsigned int				n_regulators;
 	/* Array size to be defined during init. Keep at end. */
-	struct da9063_regulator			regulator[];
+	struct da9063_regulator			regulator[] __counted_by(n_regulators);
 };
 
 /* BUCK modes for DA9063 */