hwmon: Annotate struct gsc_hwmon_platform_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 gsc_hwmon_platform_data.

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

Cc: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/20230922175053.work.564-kees@kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>

Author: kees

include/linux/platform_data/gsc_hwmon.h

@@ -40,6 +40,6 @@ struct gsc_hwmon_platform_data {
 	unsigned int resolution;
 	unsigned int vreference;
 	unsigned int fan_base;
-	struct gsc_hwmon_channel channels[];
+	struct gsc_hwmon_channel channels[] __counted_by(nchannels);
 };
 #endif