i2c: Annotate struct i2c_atr 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 i2c_atr.

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

Signed-off-by: Kees Cook <[email protected]>
Reviewed-by: Gustavo A. R. Silva <[email protected]>
Signed-off-by: Wolfram Sang <[email protected]>

Author: kees

drivers/i2c/i2c-atr.c

@@ -94,7 +94,7 @@ struct i2c_atr {
 
 	struct notifier_block i2c_nb;
 
-	struct i2c_adapter *adapter[];
+	struct i2c_adapter *adapter[] __counted_by(max_adapters);
 };
 
 static struct i2c_atr_alias_pair *