regulator: mc13xxx: Annotate struct mc13xxx_regulator_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 mc13xxx_regulator_priv.

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

Cc: Liam Girdwood <lgirdwood@gmail.com>
Cc: Mark Brown <broonie@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20230922175402.work.819-kees@kernel.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/mc13xxx.h

@@ -24,7 +24,7 @@ struct mc13xxx_regulator_priv {
 	u32 powermisc_pwgt_state;
 	struct mc13xxx_regulator *mc13xxx_regulators;
 	int num_regulators;
-	struct regulator_dev *regulators[];
+	struct regulator_dev *regulators[] __counted_by(num_regulators);
 };
 
 extern int mc13xxx_fixed_regulator_set_voltage(struct regulator_dev *rdev,